Urban Atlas

Interview Chair: WPF Transformations

2011-04-17T17:44:00.008+01:00

As a consultant I sometimes have to attend client interviews to determine whether I am right for a client or (and also to determine if the role is right for me). The experience from some of my interviews has instilled in me the need to fully understand a topic, over and beyond the surface. So, when learning new things or renewing existing knowledge, I like to put myself in the interviewee chair and ask increasingly difficult questions, peeling the layers off the topic.

Today, whilst preparing for the MCTS 70-511 certification exam, I put myself back in the chair.

Q: Do you know about WPF's ability to apply transformations to UIElement objects?
A: Sure, all UIElement derived classes can have WPF transformations applied to them.

Q: Good, do you know which property or properties of a UIElement can be set to apply a transformation?
A: The RenderTransform and LayoutTransform properties. Eg with a button you could set Button.RenderTransform to a ScaleTransform.^*

Q: OK, so what is the difference between the LayoutTransform property and the RenderTransform property?
A: Erm, the transformation set on the LayoutTransform property is applied before WPF performs lay out on the element. The transformation set on the RenderTransform property is applied before WPF renders the element.

Q: Can you elaborate on that? What's the resulting effect? Say I have some XAML with 3 buttons placed in a StackPanel and the second button has a RotateTransform applied to it, rotating it say 45 degrees. What is the effect of applying it either as a LayoutTransform or as a RenderTransform?
A: A LayoutTransform rotates the button first before laying it out. This could cause the button layout to use up more space, eg it might use up more vertical space. Elements laid out after the button will appear under the button and will not overlap in their layout. If applied as a RenderTransform however, all elements will be laid out first before the button is rotated. As a result the button's render might overlap other elements.

Q: How many transformations can I set to the LayoutTransform or RenderTransform properties?
A: Both properties only accept a single transformation object.

Q: So, if I wanted to apply a scaling and rotation to an element, how would I do that?
A: One approach would be to group both transformations under a TransformGroup element. WPF takes care of applying the transformations in the right order. You could also calculate and apply a corresponding MatrixTransform which represents the composite of the scaling followed by the rotation.

Q: That's great. If I use a TransformGroup would it matter in which order I specify my transformations?
A: Yes, the order in which the transformations are specified is important. The effect of composite transformations which involve a translation from the center of origin will be different depending on when the translation is applied.³

* LayoutTransform is actually defined on the FrameworkElement class.

Resources

[1] Transformations Overview, MSDN

[2] Adam Nathan, WPF Unleashed, Chapter 5

[3] See Remarks section, FrameworkElement.LayoutTransform, MSDN

Guidelines and rules for GetHashCode

2011-04-15T08:17:00.001+01:00

Eric Lippert provides what is bound to become the authoritative set of rules and guidelines for implementing the GetHashCode method.

Weak References in .NET

2011-04-12T14:29:00.002+01:00

Before garbage collection occurs the CLR creates an graph of reachable objects. Reachable objects are strongly referenced objects. Objects not referenced by any other object are eligible for garbage collection by the .NET Garbage Collector (GC).

Weak references are a memory management pattern which permit an object to exist in the dual state of being reachable and being eligible for garbage collection at the same time. The eventual active state of the object is time dependent. If the target object of a weak reference is accessed and converted to a strong reference before a garbage collection occurs the object will survive the collection. If collection occurs first the object will be collected.
The weak reference pattern requires wrapping a strong reference to an object in a WeakReference class and immediately setting the strong reference to null. When garbage collection occurs the GC determines if the only reference to the object is via the WeakReference instance. If that's the only reference the object is considered garbage and can be collected.
The object wrapped in a WeakReference instance is accessible via the Target property of the WeakReference class. The pattern requires checking whether the Target property returns a reference to an object or whether it returns null. The Target property returns null if the referenced object has already been GC'd.

Use case

One would only use weak references for objects that are reasonably cheap to construct but utilize a lot of memory.

Finalization and Resurrection

The mechanism behind garbage collection of objects that have a finalizer results in a phenomenom known as resurrection. When an finalizable object is identified as eligible for collection rather than immediately collecting the object, the object is placed in a special GC queue called the freachable queue. The freachable queue is a GC root and as such objects in this queue are not considered garbage because their Finalizer methods must be executed. The effect of placing a finalizable object identified as garbage in the freachable queue "resurrects" the object causing it to stay on the heap and evade collection.

Tracking resurrected objects
The weak reference pattern allows a programmer to indicate a preference for how weak references to resurrected objects is managed. This preference is specified via the WeakReference class' constructor. It is possible to pass a boolean parameter into the constructor instructing whether to track ressurections or not.

Long and Short
Weak references that do not track resurrected objects are known as Short Weak References.
Weak references track that track resurrected objects are known as Long Weak References. Using long weak references is a dangerous design because resurrected the internal state of a resurrected object is unpredictable. In any case a well designed finalizable object is likely to throw exceptions whenever an attempt is made to use it after it has been finalized.

See
[1] Weak References on MSDN
[2] Jeffrey Richter, Garbage Collection Part 2: Automatic Memory Management in .NET, MSDN Magazine

About FX Options

2011-04-09T12:57:00.001+01:00

FX options come in two flavours

Traditional options ie Call/Put
SPOT (Single Payment Option Trading)

Traditonal options

Traditonal options give the right (but not obligation) to purchase something from the option seller on a set date and price.

Eg a EUR call/USD put option gives the right to buy EUR and sell USD at the agreed price.

There's 3 types of options:

American-style: can be exercised on any day until expiration
European-style: can only be exercised on expiration
Bermudan-style: can be exercised on set dates.

Traditional options are traded OTC.

SPOT options

SPOTs allow a trader to take a view on the direction of a currency pair and pays out if the view turns out to be correct on expiry.

Eg, a trader takes the view that EUR/USD will exceed 1.300 in 1 month, buys a premium and if on expiry EUR/USD indeed exceeds the stated price the trade gets a payout.

Why trade options

Downside is limited to the premium you paid
Unlimited upside
Provides a means of hedging
Requires less capital outlay than a cash trade to gain similar exposure

Why avoid options

SPOT options cannot be traded
You may be going against the odds

Pricing Options

These factors go into pricing options

intrinsic value: this is the value of the option of it were exercised now. This value depends on whether the option is in-the-money, at-the-money, or out-of-the-money.
time value: the further the option is to expiry the more risk it carries hence the costlier the premium
interest rates: impacts on the time value
volatility: higher volatility increases the chances of the option hitting the strike price. Higher volatility implies higher premiums

References

http://www.investopedia.com/articles/trading/04/101304.asp

About Option Payoff

2011-04-09T12:48:00.003+01:00

I find options are more confusing than other derivatives. You can't think of option positions as simply being long or short. An option is either an option to buy, i.e. a Call option, or an option to sell, AKA a Put option.

A position in either option type is either long or short. So we have four option positions to reason about, long calls, short calls, long puts and short puts.

The long party on an option pays a premium to the short party. If the option expires out of the money the buyer loses their premium. The long party's potential for loss is limited to the premium but their upside potential is unlimited.

The short party on the other hand receives the option premium. The premium received is the only upside available to the option seller, and their potential for loss is virtually unlimited.

The thoughts above are helpful when thinking about the payoff of an option deal. It indicates that the long party earns zero or more while the short party loses zero or more.

For the long party, payoff P = MAX(0, difference between spot price and strike price).

For the short party, payoff P = MIN(0, difference between spot price and strike price).

This result is can be expressed more meaningfully when the option type is identified.

· A long CALL option is in the money when the spot price is greater than the strike.

· A long PUT option is in the money when the strike price is greater than the spot price.

· A short CALL option is out-of-the-money when the spot price is greater than the strike. If you are the short party to a long call option, you will lose money if your counterparty is able to exercise their option. She will only exercise it under the conditions described above, hence what's in-the-money for her is out-of-the-money for you.

· A short PUT option is out-of-the-money when the strike price is the greater than the spot price. Again, your counterparty, i.e. the holder of the long put makes money when they can sell the underlying back to you for more than it is worth in the open market.

With

P = option payoff,

S = spot price

K = strike price

P_CALL,LONG = MAX(0, S - K)

P_PUT,LONG = MAX(0, K - S)

P_CALL,SHORT= MIN(0, K - S)

P_PUT,SHORT= MIN(0, S - K)

Bond Prices: Clean and Dirty

2011-04-09T12:47:00.002+01:00

As we know, a coupon paying bond pays interest at a regular interval. This interval is typically 6 months. When a bond is priced all expected future coupon payments are factored into the price.

If a bondholder sells their bond mid way between coupon payments they would ordinarily expect to be compensated for the portion of the payment accrued since the last payment to the date the bond was sold. This makes sense. Say the bond is sold 2 months after the last coupon payment, the buyer will receive the six month coupon even though they only owned the bond for four months.

The amount accrued on the coupon in between payments is called Accrued Interest.

If the bond price includes accrued interest the price is known as the dirty price. When the price does not include any accrued interest the price is known as the clean price.

About Interest Rate Swaps

2011-04-09T12:46:00.001+01:00

An interest rate swap (IRS) contract is a deal where two parties agree to exchange payment obligations. The common case is where one party has interest payments specified as a floating rate (eg LIBOR + 50BP) but would prefer the certainty of a fixed payment interest rate. This party could enter an IRS agreement with a counterparty whereby they would pay the counterparty a fixed rate and the counterparty would pay their floating rate obligations.

Who sells them?
IRS contracts are sold by swap dealers from investment banks or other sell side financial institutions.

Who buys them?
There are 2 categories of buyers:
- Hedgers: companies with floating rate loans might prefer to eliminate the uncertainty of unknown future rates with a known fixed rate. Why wouldn't the company just get a fixed rate loan in the first place? Well, floating rate loans are cheaper than fixed rate loans. A bank would rather offer a floating rate loan because it better suits their operating models. So most companies will find it easier and cheaper to take a floating rate loan and enter a swap deal to convert it into a fixed rate loan.
- Speculators: IRS contacts enable investors to speculate on the future direction of interest rates.

How do you price one?
Pricing and valuation of an IRS depends on where we are in the life of the swap.
For a brand new swap, the issue to determine is not so much the price but the fixed rate governing the swap. The value of a new swap is expected to be zero. This makes sense, being a swap it should not initially represent a profit or loss to either party.
For an existing swap, the price is the difference between the net present value of expected fixed rate cashflows and the net present value of expected floating rate cashflows.

The long and short of it
The long party on an IRS is the party paying the fixed rate and receiving the floating rate. This is analogous to buying money at a fixed price. The short party is the one receiving fixed and paying floating. This is analogous to selling money at a fixed price.
So, if you're paying the fixed rate, you're buying, you're long. If you're receiving the fixed rate, you're receiving a payment, you're selling, you're short.

What are the risks involved?
- Market Risk: The short side is exposed to market risk. This is simply the risk of changes to interest rates. The obligations of the fixed payer (long party) is, well, fixed! She is not exposed to market risk.
- Credit Risk: It is possible that the value of the swap swings so heavily in favour of one party that the other party defaults on their obligation. Both sides are exposed to the potential of credit risk

Who's carrying the can?
From the analysis above it seems reasonable to suggest that the short side bears additional risk. Typically, a swap dealer will factor in an additional amount when determining the fixed rate that governs the deal.

Sources

[1] http://en.wikipedia.org/wiki/Interest_rate_swap#Risks

[2] http://www.investopedia.com/terms/i/interestrateswap.asp

[3] Michael Durbin, All About Derivatives, Ch 4, 9, Appendix B

What is a LIBOR reset?

2011-04-09T12:44:00.001+01:00

The daily publication of LIBOR rates is also known as a reset.
LIBOR is a fixing rate index and establishes the interate rate applicable for a range of maturities. Once published it is "fixed" or "set". The next publication (on the next business date) "resets" LIBOR.

2010-01-14T16:22:00.002Z

Remote desktop to my linux box from windows via VNC

See also: http://mail.kde.org/pipermail/freenx-knx/attachments/20080519/ce753403/attachment-0001.pdf

P/Invoke Cheat Sheet

2009-09-11T18:40:00.002+01:00

Useful cheat sheet from Tamir Khason.

Great multithreading article

2009-09-10T13:04:00.001+01:00

A comprehensive and accessible tutorial on multithreading in C# by Joe Albahari, author of LinqPad. Gradually introduces the topic leading up to advanced topics such as memory barriers and thread local storage.

SIlverlight: How to determine a control's left and top property

2009-08-09T00:23:00.002+01:00

When your control is NOT contained in a canvas it can be tricky determining it's top and left coordinates.

It turns out however that every UIElement derived control (which is virtually all controls with some visual interface) has a TransformToVisual method which allows you to acquire a transform object that can translate points relative to the controls coordinates. This allows it to transform the point (0,0) to the control's left and top coordinate values.


...
GeneralTransform generalTransform = this.TransformToVisual(null);
Point myLeftTop = generalTransform.Transform(new Point(0,0));
...

Silverlight: Hit Testing on Shapes

2009-08-08T15:50:00.015+01:00

Whilst working on a small project which required drag and drop functionality I stumbled when a templated control which I had programmed to accept drops refused to show up as a hit test item. This particular control used a rectangle to provide it's visuals.

What I had to remember was that the surface area of a shape consists of it's outline(stroke) and it's fill (if a fill is specified). My control's rectangle had an outline but did not require a fill.


<Rectangle 
    Grid.Row="1" Grid.Column="0" 
    Stroke="Pink" 
    Height="50"
    Width="50"
    StrokeThickness="5"
    MouseLeftButtonUp="Rectangle_MouseLeftButtonUp"/>

The event handler MouseLeftButtonUp is defined as below:


private void Rectangle_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
    HtmlPage.Window.Alert("Hello from Mr Rectangle");
}

With the current definition of the rectangle as it is the mouse event will only fire if you click on the shape's outline. Nothing happens if you click inside the shape.

Adding a transparent fill brings the inside of the shape into play from a hit testing perspective.


<Rectangle 
    ...
    Fill="Transparent"
    ... />

LINQ: Using SelectMany to flatten lists of lists.

2009-07-17T11:10:00.003+01:00

When you run a projection via a method which returns an IEnumerable<T> the result of your projection ends up being an IEnumberable<IEnumerable<T>>. In these cases you might actually prefer a flattened IEnumerable. Well, the SelectMany method does just that.

Eg, say you want an IEnumerable of the usages of a custom attribute in an assembly.


class AttributesReader
    {
        public static IEnumerable<MyAttributeInfo> RetrieveBAUManagedItems(Assembly assembly)
        {
            var typesInAssembly = assembly.GetTypes();
            if (typesInAssembly.Length > 0) {
                var attributesInTypes = typesInAssembly.SelectMany(type => type.GetCustomAttributes(typeof(MyCustomeAttribute), true));
            ...                
        }
    }

On the other hand simply using

typesInAssembly.Select(type => type.GetCustomAttributes(typeof(MyCustomeAttribute), true))

would return an IEnumerable<object[]>.

CodeRush Xpress for C#

2008-10-29T20:56:00.001Z

http://msdn.microsoft.com/en-us/vcsharp/dd218053.aspx

LINQ: Find duplicates

2008-07-31T22:22:00.005+01:00


var nums = new[] { 1,2,2,4,5,5,6,7,8,8,8,9 };
var distinct = nums.Distinct();

if(nums.Count() != distinct.Count())
{
   nums.GroupBy(n => new { DuplicatedNumber = n })
       .Where(g => g.Count() > 1)
       .Select(g => new { number = g.Key.DuplicatedNumber, numberOfDuplicates = g.Count() }).Dump("Duplicates found");
}
else
{
   "No duplicates found".Dump();
}

ps: Get yourself a copy of the excellent free LINQPad and enjoy the wonders of the BIG Dump()!

Javascript Libraries

2008-06-11T09:32:00.002+01:00

I have been reluctant to invest some time learning any particular Javascript library because I fear that it might be extremely time consuming to master, and it might result in weighty pages and expensive bandwidth utilization having clients downloading very large .js files.

I am however coming round to the idea that the productivity gains might be a worthwhile trade-off.

So, which library should I start with? Dojo? JQuery? Prototype? Ext? Is there enough cross over between these libraries such that learning one gives a good grounding for getting into the others?

Anyone kind enough to advise?

Thanks

Turtles at the Huntington Botanical Gardens, CA

2008-04-24T10:23:00.000+01:00

Old flour mill in Bristol

2008-04-22T17:07:00.000+01:00

Christo Rei, Lisbon

2008-04-20T09:50:00.000+01:00

Headmistress' Office, Nigerian village school

2008-04-19T13:56:00.000+01:00

Prince's Wharf Bristol

2008-04-16T09:00:00.000+01:00

Bristol Balloons

2008-04-14T08:39:00.000+01:00

Welcome to Alata

2008-04-13T11:19:00.000+01:00

Welcome sign at the idyllic Alata village in the Nigerian city of Ibadan.

Porta da Traicao, Castelo dos Mouros Sintra

2008-03-06T19:53:00.001Z

Mundo Dakar

2008-03-05T18:10:00.000Z

Restaurante Ponto Final

2008-03-04T18:08:00.000Z

Bryce Canyon National Park, Utah

2008-03-03T20:40:00.000Z

Museu de Arte Moderna, Sintra

2008-03-02T10:28:00.001Z

Christo Rei

2008-03-01T01:02:00.000Z

Ubehebe Crater, Death Valley

2008-02-28T17:56:00.000Z

Don't eat seeds

2008-02-27T17:49:00.001Z

Directions

2008-02-26T20:02:00.003Z

Badwater Basin, Death Valley National Park

2008-02-25T09:53:00.000Z

Futebol Clube de Lisboa

2008-02-24T17:19:00.000Z

Proud Arizonian momma

2008-02-23T00:10:00.002Z

Echinopsis Robinsoniana

2008-02-21T17:45:00.001Z

Padrão dos Descobrimentos

2008-02-20T21:43:00.001Z

Open Handset Alliance

2007-11-06T08:35:00.000Z

The mobile space just got more interesting! Google and friends announced the Open Handset Alliance which is a new open mobile phone platform. The SDK, named Android, will be announced on 12 Nov 2007. The OHA expects the have commercial devices and applications deployed in the second half of 2008.

Determine HTTP version from HttpRequest in ASP.NET

2007-10-02T12:16:00.000+01:00

You can determine which HTTP version a request was composed with via the HTTP_VERSION or SERVER_PROTOCOL server variables. Ie,


using System.Web;
string httpVersion;
// and one of these:
httpVersion = HttpContext.Current.Request.ServerVariables["HTTP_VERSION"];
httpVersion = HttpContext.Current.Request.ServerVariables["HTTP_PROTOCOL"];

The SERVER_PROTOCOL header should return "HTTP/1.0" or "HTTP/1.1"

Hexadecimal in C#

2007-09-07T14:58:00.000+01:00

The easiest way to convert numbers and bytes to hexadecimal is the ToString method.

Eg
byte input = 35;
string hexString = input.ToString("X", System.Globalization.CultureInfo.InvariantCulture);

Some other useful ways are described in this thread.

Enchanting music

2007-08-22T11:55:00.001+01:00

I'm still basking in the brilliance of the Beginner's Guide To World Acoustic 3CD ablum I bought the other week. It has exposed me to a lot of music that I hadn't previously experienced.

One of my new favourite singers is the Ladino star aka Yasmin Levy. Her track Naci En Alamo leads the second CD, and my God, does she have an enchanting voice. I just can't seem to get enough of her voice. The track is really soul stirring, energizing and evocative. I am now looking for a digital retail outlet where I can download her highly rated album La Juderia.

Refreshing music

2007-08-21T20:15:00.000+01:00

I recently discovered the scintillating voice of Sara Tavares, a Portuguese singer of Cape Verdan descent. Amazing voice, absolutely stunning lady. The single Lisboa Kuya was included in The Beginner's Guide To World Acoustics multidisc album which I bought the other day.

Also in the same album was Loucura - an enchanting piece by another Portuguese stunner called Mariza. Apparently she is world famous, and deservedly so. I loved her voice and proceeded to purchase her album Fado Em Mim.

After weeks of consuming mass market pop music it's essentially reviving to encounter great music from some amazing musicians.

10 Totally Stupid Online Business Ideas That Made Someone Rich

2007-08-08T19:59:00.000+01:00

An interesting post on nichegeek.com. Enjoy!

Internet usage trends from the States

2007-08-08T17:29:00.000+01:00

An interesting report from Business Week identifying how different age demographics consume the internet in the US.

Pew Global Attitudes Project

2007-08-07T22:21:00.001+01:00

This report from Pew Research Centre is the most interesting and informative article I have seen this year.

Noteworthy are the findings that

there is a sharp decline in support for terrorism in Muslim countries
there is great optimism in Africa with people expressing the belief that whilst the present times are bleak, future generations will be better off
there is an increase in the quality of life all over the world with the exception of Western Europe and the USA
Western Europeans and Americans are generally unhappy with the state of their nations whilst the rest of the world is happier than in 2002
GDP has risen in all regions, rising fastest in Eastern Europe and slowest in Western Europe.

Another reason why women are very important

2007-08-07T21:33:00.000+01:00

According to trendwatching.com:

[Women] comprise just over 50% of the US population, make over 80% of the consumer purchasing decisions (and in case you're wondering, consumer spending accounts for two-thirds of US GNP). Consulting firm A.T. Kearney estimates that women determine 80 percent of consumption, purchase 60 percent of all cars and own 40 percent of all stocks.

-http://www.trendwatching.com/trends/femalefever.htm

2007 Top 100 Global Brands

2007-08-03T08:40:00.000+01:00

BusinessWeek and Interbrand has released the 2007 rankings of global brands.

US companies again show their strength with 52 of the top 100 being American. The first 4, and 7 out of the top 10 are from the US.

The highest ranking UK company was HSBC at position 23. However we dominated the bottom 25 with 5 of our companies in positions 76 to 95.

Border Gateway Protocol

2007-07-26T09:25:00.000+01:00

BGP is a routing protocol on the internet.

en.wikipedia.org/wiki/BGP

Energy consumption

2007-07-25T23:45:00.000+01:00

Computers in American offices burn $1 billion worth of electricity annually - and that's when they're not producing a lick of work.

Source: TIME Magazine (Jul 16 2007)

Hello Buster!

2007-07-02T19:46:00.000+01:00

Here's Buster, a rideable vacuum cleaner designed to get kids helping out at home. Nice!!

http://www.yankodesign.com/index.php/2007/06/18/rideable-vacuum-cleaner-by-kristina-andersson/

Mobile Phone Web Server

2007-06-19T20:24:00.000+01:00

Nokia have released a web server that runs on your mobile phone enabling you to host your blog and other content directly on your mobile phone.

A chick called Darla Mack is running the server on her N95 using GPRS connectivity. I also installed the server on my N95 but I used Wifi connectivity.

Download it free here.

Cuddly Cactus

2007-06-18T23:05:00.000+01:00

Espostoa Ritteri - Taken at Huntington Gardens, CA.

Cost of Living Survey (for expatriats)

2007-06-18T13:26:00.000+01:00

Moscow is the world’s most expensive city for expatriates for the second consecutive year, according to the latest Cost of Living Survey from Mercer Human Resource Consulting.

Australian Obesity

2007-06-16T21:58:00.000+01:00

67% - Proportion of Australian men who are overweight.

Source: TIME magazine (9 Apr 2007)

Half Nelson: Review

2007-06-15T08:36:00.000+01:00

Half Nelson lived up to expectations. It was a simple telling of the complexity aka human living. The story of a gifted, well meaning, motivational young teacher caught up in the devils of drug addictions. The story of the contradictions of life and living.

Half Nelson is an exploration of the study of change brought about by opposing forces. The film proposes that opposites do not necessarily have to be exclusive but many reside within the same space. I.e it is possible to have good and bad living together in the same person. Kindness and wickedness can be found in the same heart. Being one thing does not automatically exclude us from being the opposite thing. The thinking suggests that we are wrong to insist on a one box per person/situation policy.

This is seen in the storyline with Ryan Gosling's character Dan Dunne. You see his eagerness to provide a good example to his students but you also see his personal weaknesses. His teaching style also exposed a contradiction - he wants to give them an education but also wants them to have fun. But, is that really contradictory? The storyline is full of these little "contradictions".

This is no complete end to end story. It's just a peek into one life. It's a story of despair mingled with hope but it doesn't end with any salvation. We are left with a life that's still full of it's contradictions and difficulties, but at the same time riddled with some hope.

Half Nelson leaves you with a mixture of emotions - you laugh, you smile, you wonder, you hope, you feel pain and disgust. But this is life.

Great performances by Ryan Gosling and Shareeka Epps make this film by rookie director Ryan Fleck a thoroughly watchable and believable contribution.

Half Nelson

2007-06-14T09:02:00.000+01:00

I'm going to see the acclaimed Half Nelson this evening.