how to do convolution without commands

48 次查看（过去 30 天）
omar chavez
omar chavez 2011-11-27
评论： Sai Jothsna Sri 2023-9-7
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

请先登录，再回答此问题。

采纳的回答

Chandra Kurniawan
Chandra Kurniawan 2011-11-27
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
>>
  1 个评论
David Young
David Young 2011-11-27
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.

请先登录，再进行评论。

更多回答（5 个）

Wayne King
Wayne King 2011-11-27
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)
  1 个评论
omar chavez
omar chavez 2011-11-27
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

请先登录，再进行评论。

DI
DI 2015-3-16
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...
SALVADOR CANAS
SALVADOR CANAS 2018-1-15
Those convolutions are convolutions with padding=1, how do you do for padding=0?
Sk Group
Sk Group 2021-10-25
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/
VIGNESH B S
VIGNESH B S 2022-7-28
Ran in:
% 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)

类别

在 Help Center 和 File Exchange 中查找有关 Programming 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by