Unable to find an entry point named 'xxx' in DLL 'xxx.dll' exception?

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C#

DLL

MatLab

Hi I have prepared a simple matlab code and deployed it by means of deployment procedure in matlab in ".Net assembly" type (for use in C#.net 2010). The output Dll file of matlab was named "main". But that error occurs. I have added references.
What I really want is to define variables and give values to them in C# environment, calculate the outputs in Matlab Dll file, and finally show the results in C#.

Matlab Code:

function c=main(a,b)
c=a+b;
end

C# code:

namespace WindowsFormsApplication1
{
public partial class form1.form
{
[DllImport("main.dll")]
public static extern int main (int a, int b);

public form1()
{
InitializeComponent();
}
private void button1_click(object sender, EventArgs e)
{ 
int a,b,c;
a=convert.toint16(textbox1.text);
b=convert.toint16(textbox2.text);
c=main(a,b);
textbox3.text=c.ToString();
}
}
}