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Using Matlab from a C# application

, 17 May 2013
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Using Matlab from a C# application.

During writing application for my Masters degree diploma I wrote simple application that was using COM Matlab server. I have found hard to using it mainly to lack of documentation, which is really basic with only few code examples for C#. I guess writing programs that use Matlab for calculating is not encouraged by MathWorks, you would became competition that way Smile. Nonetheless I accomplished why I have required to do so I decided to share this with rest of the world.

Important: I was using R2010a version of Matlab. I realize that there is newer version. But I had only this version at my disposal. Since interface for communicating with Matlab server is dependent of installed Matlab version and registry entries it may have been different with yours. But I suspect not to much. I also tries with 7.1 and (if I remember correctly) it required only to swap reference in Visual Studio. But again... it was only test so there might be other problems that I am not aware of.

Let's start with simple console application. Lets call it MatlabTest. First we will add dll reference with COM interface. Click RMB on project and choose [Add Reference] option. In new window click COM tab. In search text box write 'Matlab'. Then choose "Matlab Application (Version 7.10) Type Library".

You should get new reference like below:

Great. Now we should test if it is working. In order to use it we should create our Matlab server from C# application. To that we can add code to our main program:

var activationContext = Type.GetTypeFromProgID("matlab.application.single");
var matlab = (MLApp.MLApp)Activator.CreateInstance(activationContext);
Console.WriteLine(matlab.Execute("1+2"));
Console.ReadKey();

This code will create single Matlab COM server through Activator class. Program Id "matlab.application.single" means single Matlab COM server for our application. When it will try to create another Matlab, it will just return reference to the same object. Contrary to that we could use "matlab.application" which will create another instance of Matlab any time Activator.CreateIntance method will be executed. In more complex applications or for web applications or other programs which run for long time it may creates big memory leaks since 1 instance cost around 220 Mb (on 64 bit Windows 7 and Matlab R2010a).

After creating Matlab program execute simple sum of 2 integers, just for test of communication we don't need anything more sophisticated. It should return also simple string in console:

It's really simple and more important it works! Smile

This way we can send and receive string messages with MATLAB only. It's not much useful. Also there is one way to find out if our statement had errors. It will have 'error' string in response.

Let's try to run something like this: '1*', which will result in error:

So to check our command had errors we have to check if output string have "??? Error" in it.

To send some parameters along with our command we have to use on of 'Put*' methods. Best is one called PutWorkspaceData. It takes three parameters. First is desired name of our new Matlab variable. Two other are much more tricky. To set variable correctly (so you could reference it in command) you must use global workspace. But it is called? This one took much more time then I would want. It is not mentioned in documentation of this method. If I remember it right I found it in some code example and it should be only "base". In the end I created in my application another method that encapsulated PutWorkspaceData and forget about it Smile. Third parameter is value of our variable. It should be simple. Let's change our code to:

matlab.PutWorkspaceData("a", "base", 2);
Console.WriteLine(matlab.Execute("a*a"));

Result will as below:

But it is just int. What about more complicated structures? How about multiplication of two vectors? Matlab is using .NET type double to send and receive information with our application. Again I did not find it anywhere in documentation, but rather reverse engineered this from data returned from Matlab.So let us try send 2 arrays of doubles. and multiplicate them in Matlab. First will be named 'a' and second 'b'. Matlab command will be "a'*b". Transposition will give us nice matrix instead for single number.

matlab.PutWorkspaceData("a", "base", new[]{2d,3d,1d});
matlab.PutWorkspaceData("b", "base", new[]{4d,3d,2d});
Console.WriteLine(matlab.Execute("a'*b"));

And in return we will get:

Next step will be to return this output to our console app. To do that we can use GetWorkspaceData that works similar to PutWorkspaceData or... we can use GetVariable method. This one returns dynamic so our application needs to run on .NET 4. It takes to parameters name of variable we want to return from Matlab and again name of workspace. You really should save this string as const somewhere Smile. Change our code to:

matlab.PutWorkspaceData("a", "base", new[]{2d,3d,1d});
matlab.PutWorkspaceData("b", "base", new[]{4d,3d,2d});
Console.WriteLine(matlab.Execute("c=a'*b"));
var c = matlab.GetVariable("c", "base");

After that in our console app we will have variable c and it will be two dimensional array of doubles. To show values of this array in console we can just iterate it with simple foreach loop. But instead that we will iterate two of the dimensions. This will give us info about values and dimensions of this matrix.

for (var i = 0; i < c.GetLength(0); i++)
{
   for (var j = 0; j < c.GetLength(1); j++)
        Console.Write(c.GetValue(i, j) + " ");
   Console.WriteLine();
}

Ok.That was matrix. How about vectors? Luckily vectors are for Matlab just special case of matrix so it will spit out two dimensional array also. More complex is case of empty matrix. No it is not null. It would be to easy. Instead it is special type Missing. I guess it have some logic behind. Null would indicate that variable have no value at all or this is not defined. But we have empty matrix so this is not defined nor this is lack of value. So why not just array with zero values in it? No idea.

Lets try run code like below to test it:

Console.WriteLine(matlab.Execute("c=a'*b"));
Console.WriteLine(matlab.Execute("d=[]"));
var c = matlab.GetVariable("c", "base");
var d = matlab.GetVariable("d", "base");
for (var i = 0; i < d.GetLength(0); i++)
{
   for (var j = 0; j < d.GetLength(1); j++)
      Console.Write(d.GetValue(i, j) + " ");
   Console.WriteLine();
}

Running those command in Matlab will work just fine. Instead of that error will be throwed on first for loop:

Not very nice. To prevent this errors application have to check if dynamic type returned from matlab is in fact empty (Missing). Not very clean it is better to wrap this in other method that will perform this check for us whenever we want to get our data from Matlab. In my project I ended up writing few methods for returning vectors, matrices, numbers, strings etc. Vector one looked like this:

public static Vector GetVector(this MLApp.MLApp matlabComObject, string variabla_name)
{
    var dynamicVariable = matlabComObject.GetBaseWorkSpaceVariable(variabla_name);
    var dataList = new Vector();

    if (TypeChecker.IsVector(dynamicVariable))
    {
        dataList = Vector.DynamicToVector(dynamicVariable);
    }
    else if (TypeChecker.IsNumber(dynamicVariable))
    {
        dataList.Add(dynamicVariable);
    }
    else if (TypeChecker.IsEmptyMatrix(dynamicVariable))
    {
        //do nothing empty vector or matrix ([0x0] or [1x0])
    }
    else throw new Exception(string.Format(
      "Type of dynamic variable ({0}) is not supproted!", dynamicVariable.GetType()));
    return dataList;
}

TypeCheker checks for type of dynamic. It's pretty straightforward. For our Missing type it's just one line:

public static bool IsEmptyMatrix(object dynamicVariable)
{ return dynamicVariable.GetType() == typeof(Missing); }

After checking type of dynamic we can just cast it to another type to take advantage of static properties of language. Why use dynamic at all? First I think that ref and out method parameters are messy and second: I prefer 

var d = matlab.GetVariable("d", "base");

from

object e;
matlab.GetWorkspaceData("d", "base", out e);

It is only 1 line. And since object you have to create first and then cast it also don't bother and just use dynamic. But I guess it is just what will you like better.

String are much more friendly and there are just string. Or null. Smile

Now we know how to put and get data from Matlab. How to execute commands and check them for errors.

If you executed any of these example you probably take notice of very simple Matlab window which have opened during life of your console app. If you terminate it by disabling debugging or it will close due to error, Matlab window will remain opened. If not it will close nicely with console window. But still it huge memory leak risk if no maintained properly. To that I recommend creating some special class that will create instance or instances of Matlab. It should track or of created instances and in case anything bad happens (but dynamic variable cast is probability Smile) it will close all instances prior of application exit. Tracking should be employed through WeakReference class, so whenever Garbage Collector would want to destroy Matlab instance it should not be stopped by our tracking class. To destroy COM instance we can use method Marshal.FinalReleaseComObject. So with weak reference code for that will look like this: 

public static void Release(WeakReference instance)
{
    if (instance.IsAlive)
    {
        Marshal.FinalReleaseComObject(instance.Target);
    }
}

Method Quit of matlab server instance does not close it immediately and code above will.

If you want to hide that popup Matlab window you can set this in it's instance:

matlab.Visible = 0;

This way it will fade away and run as service.

This most basic info about Matlab in C#, but it will get you started. So happy coding. Smile

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

n.podbielski
Software Developer
Poland Poland
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Comments and Discussions

 
Questionmatlab function from c# PinmemberMember 1095446118-Jul-14 11:51 
AnswerRe: matlab function from c# Pinmembern.podbielski30-Jul-14 4:03 

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