how to do convolution without commands

Hi, im trying to do convolution without any of the commands in matlab.

Just plain for, this is because im trying to use a code that can also be implemented on C.

So far I have this

    x=[1 2 3]  
      h=[-1 0 3]
      Z=[0]
      [M,N]=size(x)
      [L,O]=size(h)

      A=N+O-1

      for n=1:1:N
          for o=1:1:O
              y(n,o)=x(n)*h(o)

          end 
      end

[Sai Jothsna Sri]

sreya sathe

Answer 1

[Chandra Kurniawan]

Hi, Omar. Do you seeking for 2D convolution code without Matlab toolbox command?? I have the code below

function B = convolve(A, k);
[r c] = size(A);
[m n] = size(k);
h = rot90(k, 2);
center = floor((size(h)+1)/2);
left = center(2) - 1;
right = n - center(2);
top = center(1) - 1;
bottom = m - center(1);
Rep = zeros(r + top + bottom, c + left + right);
for x = 1 + top : r + top
    for y = 1 + left : c + left
        Rep(x,y) = A(x - top, y - left);
    end
end
B = zeros(r , c);
for x = 1 : r
    for y = 1 : c
        for i = 1 : m
            for j = 1 : n
                q = x - 1;
                w = y -1;
                B(x, y) = B(x, y) + (Rep(i + q, j + w) * h(i, j));
            end
        end
    end
end

Save the following code with filename 'convolve.m'. And then create a new m-file and type this code :

clear; clc;
I = [4 4 3 5 4;
       6 6 5 5 2;
       5 6 6 6 2;
       6 7 5 5 3;
       3 5 2 4 4];
k = [0 -1 0;
        -1 4 -1;
        0 -1 0];
Hsl = convolve(I, k)

Watch at the result! You can also compare the result with the matlab toolbox command 'conv2'

Bnd = conv2(I,k,'same')

The both results are same :

Hsl =

       6     3    -2     8     9
       9     3     0     2    -3
       2     0     2     6    -3
       9     6     0     2     1
       1     8    -6     5     9

Bnd =

       6     3    -2     8     9
       9     3     0     2    -3
       2     0     2     6    -3
       9     6     0     2     1
       1     8    -6     5     9

>>

[David Young]

This is a little more complex than necessary - you don't need the first loop that reflects A, just change the index computation in the second loop to reflect the mathematical definition of convolution.

Answer 2

[Wayne King]

I take it when you say "without commands", you really are just saying without conv(). It appears to me you have 1-D vectors from your initial post. Specifically, you give the example:

x=[1 2 3];
h=[-1 0 3];

You can exploit the relationship between linear convolution, circular convolution, and the DFT by extending the length of your input vectors with zero-padding, multiplying their DFTs, and then taking the inverse DFT.

x = [1 2 3]';
h = [-1 0 3]'; 
N = length(x)+length(h)-1;
x1 = [x; zeros(N-length(x),1)];
h1 = [h; zeros(N-length(h),1)];
convxh = ifft(fft(x1).*fft(h1));

Compare convxh with

conv(x,h)

[omar chavez]

yes you are right. The thing is that, since the code should be able to apply in several platforms I cant use ifft or fft. Im trying to prove that a code can be put in several languages, like matlab, C,etc

Answer 3

[DI]

The first answer is not actually full size.

Full size will be like this:

% Written by Dizeng 3/15/2015.  Full convolution.
function B = convolve(A, k) 
[r,c] = size(A);
[m,n] = size(k);
h = rot90(k, 2);
center = floor((size(h)+1)/2);

Rep = zeros(r + m*2-2, c + n*2-2);
for x = m : m+r-1
    for y = n : n+r-1
        Rep(x,y) = A(x-m+1, y-n+1);
    end
end
B = zeros(r+m-1,n+c-1);
for x = 1 : r+m-1
    for y = 1 : n+c-1
        for i = 1 : m
            for j = 1 : n
                B(x, y) = B(x, y) + (Rep(x+i-1, y+j-1) * h(i, j));
            end
        end
    end
end

Hope it will be helpful to others...

[Maryam Soltanlou]

why do you use + in 'loop'? h(x,y)=int(M(m-i,n-j)k(i,j)didj

[Savannah Quinn]

I am getting an index out of bounds due to h(i,j)

[Enrique de José María Flores Rodríguez]

Seem works good on a DICOM image on 2021, thank you !

Answer 4

[SALVADOR CANAS]

Those convolutions are convolutions with padding=1, how do you do for padding=0?

Answer 5

[Sk Group]

Convolution without Function in MATLAB

Convolution without conv function in MATLAB | Complete CODE | Explanation | Example And Output

For complete detailed post visit: https://www.swebllc.com/convolution-without-function-in-matlab/

Answer 6

[VIGNESH B S]

% The code below is for convolution without conv command.
% Idea behind it is multiplying a element of x with every element in h and
% adding them with a shift. 

% Eg: x = [1,2] and h = [4,5,6] say, h is transformed to [3,4,5,0] ; no.of 
% zeros to add after h is given by min(len(x) ,len(h)) -1). als zero is
% added so problems with vector addn is removed. (ouput of conv is of same
% length as transformed h). 

%then you perform x(1).*h = [4,5,6,0] and x(2).*h = [8,10,12,0] when x(i)
%if i>2 -> you add zeros to the result of x(i).*h in at index 1 and shift
%it.       y = conv of x and h = [4,5,6,0] + [0,8,10,12].

clc
clear
 
x = input('Enter x [..] '); %getting input x and h

Unable to run the 'fevalJSON' function because it calls the 'input' function, which is not supported for this product offering.

h = input('Enter h [..] ');
 
if length(x)>length(h)
   temp_var = x;
   x = h;
   h = temp_var;
end
 
y = zeros(1,(length(x)+length(h)-1));
min_val = [length(x),length(h)];
r = min(min_val)-1;  ;%minimum of x and h -1
hi = [h,zeros(1,r)];
 
 
for i = 1:length(x)
    temp = x(i).*hi;
   % disp(temp)
    if i>=2
        tempi = [zeros(1,i-1),temp(1:end-i+1)];
    else
        tempi = temp;
    end
    
   y = y + tempi;
end
disp('The convolution of x and h is:' );
disp(y)