DSP - Auto Correlation (Scilab Code with Plot)

Scilab Code:

//Auto Correlation of x(n) is given as:

//R(k) = summation of x(n)*x(n-k) for n = -INF to INF

//Position of origin in the given sequence doesn't matter,

//Its only taken to plot the given sequence.

clc; close; clear;

x = input("Enter the sequence: ");

x_origin = input("Enter the position of origin in the sequence: ");

//plot the given sequence

subplot(2,1, 1);

x_lower = -(x_origin - 1);

x_upper = length(x) - x_origin;

n = x_lower : x_upper;

plot2d3(n, x, style=color("red"));

xtitle("x(n)","n");

a = gca();

a.children.children(1).thickness = 2;

a.y_location = "origin";

//plot the auto correlation

subplot(2,1, 2);

L = length(x);

n = -L+1:L-1;   //Elsewhere it'll be 0

y = xcorr(x);

disp(y, "Auto Correlation = ");

plot2d3(n, y, style=color("blue"));

xtitle("Auto Correlation of x(n)","n");

//The above code can also be done as follows:

//[y, ind] = xcorr(h);

//plot2d3(ind, y);

//No need to define the range.

a = gca();

a.y_location = "origin";

a.children.children(1).thickness = 2;

Console I/O:

Plot:

DSP - Circular Convolution of Discrete Time Signals (Scilab Code with Plot)

Scilab Code:

//Circular Convolution of x(n) and h(n) is given by:

//Summation of x(n).h(m-n) from 0 to N-1

//where, N = length of sequences

//Both the sequences start from the origin

clc; close; clear;

x = input("Enter the first sequence: ");

h = input("Enter the second sequence: ");

//perform zero-padding to make lengths equal

length_diff = length(x) - length(h);

if length_diff>0 then

    h = [h, zeros(1:abs(length_diff) )];

else

    x = [x, zeros(1:abs(length_diff) )];

end

x_origin = 1;

h_origin = 1;

x_lower = -(x_origin - 1);     //lower range of x

h_lower = -(h_origin - 1);     //lower range of h

x_upper = length(x) - x_origin;     //upper range of x

h_upper = length(h) - h_origin;     //upper range of h

//Create the x_matrix and h_matrix

len = length(x);

for i = 1:len

    x_mat(i, 1) = x(i);

    j = i;

    for c = 1:len

        h_mat(j, i) = h(c);

        j = j + 1;

        if j == (len+1)

            j = j - len;

        end

    end

end

y = h_mat * x_mat;

y = y';

disp(x, "x = ");

disp(h, "h = ");

disp(x_mat, "x_mat = ");

disp(h_mat, "h_mat = ");

disp(y, "Circular Convolution = ");

subplot(3, 1, 1);

plot2d3(x_lower:x_upper, x, style=color("green"));

xtitle("First Sequence","n","x(n)");

a = gca();

a.x_location = "origin";

a.y_location = "origin";

a.children.children(1).thickness = 2;

subplot(3, 1, 2);

plot2d3(h_lower:h_upper, h, style=color("red"));

xtitle("Second Sequence","n","h(n)");

a = gca();

a.x_location = "origin";

a.y_location = "origin";

a.children.children(1).thickness = 2;

subplot(3, 1, 3);

n = 0:(len-1);

plot2d3(n, y, style=color("blue"));

xtitle("Circular Convolution: x(n) x h(n)","n","y(n)");

a = gca();

a.x_location = "origin";

a.y_location = "origin";

a.children.children(1).thickness = 2;

Console I/O:

Plot: