I have created a function lpf which uses fdesign.lowpass,design and filter functions.Then builded a C++ Dll to call this lpf function from VC++.Function is returning zero everytime in an array of size 100.I have pasted the code for description

MAT LAB Version 7.0.0.19920 (R14)

Data passed(100 values) to function lpf and lpf1.

x=[10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20,10,5,100,50,20]

Other Parameters passed are

Order n = 2

CutOff frq fc = 3

Sampling Rate s = 20

I am Using lpf function as following

 function z=lpf(x,n,fc,s)
 hl  = fdesign.lowpass('N,Fc', n, fc, s);
 Hdl = design(hl, 'butter');
 z=filter(Hdl,x);

It is executing fine from matlab command window.Now i builded dll to use it in VC++ and then called from Vc++,function is returning always zero in an array.

To crosscheck I used lpf1 function as following

 function y=lpf1(x)
 b=[1  2  1];
 a=[ 1  -0  0.17157287525381];
 y=filter(b,a,x);

This function executed fine in matlab command window.Then i builded dll to use it in VC++,I got the desired result with filtered values in an array.

So my question is why lpf is not working but lpf1 is working when calling both functions from VC++ after building dll in matlab.

What is the reason that lpf is returning always zero in an array in VC++ but filtered or desired output in matlab command window.

[Oleg Komarov]

Please format the code http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup.

Also, change the title of your question to something short and meaningful.

Finally retag your question http://www.mathworks.com/matlabcentral/answers/43073-a-guide-to-tags

Those changes will make it likely that somebody answers.