How can i convolve a unit ramp and unit step signal without using the 'conv' code ?

function [a,b,m,sum] =convsamp( h )

 m=0:h; 
 a=[0,(0:h)]; %unit ramp sequence
 b=[0,ones(1,h)]; %unit step sequence
 sum =(h+h)-1;
   for i=0:(h+h)-1
      y(i)=0; 
        for j=0:h
            if(i-j+1>0) 
              y(i)=y(i)+a(j)*h(i-j+1); 
            end 
        end 
   end
subplot(3,1,1), stem (m,b), %plots the step signal
title('Unit Step Sequence');
subplot(3,1,2),stem(m,a), %plots the ramp signal
title('Unit Ramp Sequence');

---i used this code but there seems to be a problem in line 6 y(i)=0; can you please help me

Answer 1

[Guillaume]

An easy way to implement a convolution without using conv is to implement the convolution theorem:

function c = myconv(a, b)
    len = numel(a) + numel(b) - 1;
    c = ifft(fft(a, len) .* fft(b, len));
end

Probably faster than the built-in conv as well.

[Deborah Montojo]

Thank You Guillame

Answer 2

[Jan]

It is not exactly "there seems to be a problem", but you get a real error message. Then please post it completely instead of letting the readers guess the problem.

sum =(h+h)-1;

This variable is not used anywhere. In addition shadowing the builtin function "sum" is a bad idea, because this causes unexpected behavior frequently, when you want to access the function later.

   for i=0:(h+h)-1
      y(i)=0;

In the first iteration you try to access y(0), but indices must be greater than 0. The error message explains this clearly. Use this instead:

   y = zeros(1, 2 * h);  % Pre-allocation
   for i = 1:(h+h)
      % y(i)=0;  % Can be omitted

A pre-allocation is essential, because the iterative growing of arrays wastes a lot of resources. Search in the forum for details.

[Deborah Montojo]

Thank you Jan Simon

[Deborah Montojo]

This is the problem:

Create a function similar to convolution using if/while/for loops.

Plot a ramp signal and a unit step signal.

Using the convolution function you created, find the convolution of the two signal.

Plot the output convolution, unit step and ramp signal in a figure using subplot.