Why I am unable to run my program?

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Hi, I really need help. I cannot run my program. When I run, it shows ' Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 121-by-1'. Please, I really need help.

%Parameters to define the governing casson fluid equation and the
%parameters value range
L = 1; % Length of the artery
maxk= 10; % Number of time steps
tmax = 0.1; % Maximum time
delta_t = tmax/maxk; % Time step
n = 10; % Number of space steps
delta_r = L/n; % Radial direction
Beta1 = 0.025; % Casson fluid parameter
A0 = 0.2; % Amplitude of systolic pressure gradient
A1 = 0.4; % Amplitude of diastolic pressure gradient
omega = pi/4;
%Initial conditions of velocity
for i = 1:n+1
    u(i,1) = 0;
    disp(u(i,1));
end
% Boundary conditions
for j=1:maxk+1
    u(1,j) = 0;
    u(n,j) = 0;
end
% Implementation of the explicit
for j=1:maxk % Time Loop
for i=2:n % Space Loop
S10 = (u(2,j)-2*u(1,j)+u(2,j))/((delta_r)^2);
S20 = (u(2,j)-u(1,j))/(delta_r);
    u(1,j+1) = u(1,j) + delta_t*(A0 + A1*cos(omega*t) + Beta1*((S10) + 1/r* (S20)));
disp(u(1,j+1))
S1 = (u(i+1,j)-2*u(i,j)+u(i-1,j))/((delta_r)^2);
S2 = (u(i+1,j)-u(i,j))/(delta_r);
    u(i,j+1) = u(i,j) + delta_t*(A0 + A1*cos(omega*t) + Beta1*((S1) + 1/r* (S2)));
disp(u(i,j+1))
S1n = (u(n+1,j)-2*u(n,j)+u(n-1,j))/((delta_r)^2);
S2n = (u(n+1,j)-u(n,j))/(delta_r);
    u(n,j+1) = u(n,j) + delta_t*(A0 + A1*cos(omega*t) + Beta1*((S1n) + 1/r* (S2n)));
disp(u(n,j+1))
end
end
%Graphical representation of the velocity at different selected times
plot(u);
%figure(1)
%plot(u(:,1),r,'-',u(:,2),r,'-',u(:,3),r,'-',u(:,6),r,'-')
%tittle('velocity within explicit method')
%xlabel('r')
%label('u')
%legend('dt=1','dt=2','dt=3','dt=6')

2 Comments
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John D'Errico on 28 Dec 2021

Edited: John D'Errico on 28 Dec 2021

When you get an error, don't just tell us what you personally think is important. The fact is, you don't know what is important. else you would not be asking this question.

Paste in the COMPLETE error message. EVERYTHING in red. That will tell us which line was the problem. It would allow us to learn that without trying to run your code, stepping through every line to see when it fails, IF it fails.

Anyway, we cannot even try to run your code, since I see the variable t was never defined. So it is not possible to answer your question at the moment. My guess is your problem may be that t is a vector. But how do I know?

If you want help, is there a reason why you would want to make it more difficult (and even impossible) to get help?

VBBV on 28 Dec 2021

There is no error if you assign correct values to variables r and t

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Answer 1

Image Analyst on 28 Dec 2021

Open in MATLAB Online

0 votes

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clearvars;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fprintf('Beginning to run %s.m ...\n', mfilename);
%Parameters to define the governing casson fluid equation and the
%parameters value range
L = 1; % Length of the artery
maxk= 10; % Number of time steps
tmax = 0.1; % Maximum time
% Define t and r
allTimes = linspace(0, tmax, maxk)
r = 1; % Whatever...?????
delta_t = tmax/maxk; % Time step
n = 10; % Number of space steps
delta_r = L/n; % Radial direction
Beta1 = 0.025; % Casson fluid parameter
A0 = 0.2; % Amplitude of systolic pressure gradient
A1 = 0.4; % Amplitude of diastolic pressure gradient
omega = pi/4;
%Initial conditions of velocity
for i = 1:n+1
    u(i,1) = 0;
    disp(u(i,1));
end
% Boundary conditions
for j=1:maxk+1
    u(1,j) = 0;
    u(n,j) = 0;
end
% Implementation of the explicit
for j=1:maxk % Time Loop
    t = allTimes(j);
    for i=2:n % Space Loop
        S10 = (u(2,j)-2*u(1,j)+u(2,j))/((delta_r)^2);
        S20 = (u(2,j)-u(1,j))/(delta_r);
        u(1,j+1) = u(1,j) + delta_t*(A0 + A1*cos(omega*t) + Beta1*((S10) + 1/r * (S20)));
        disp(u(1,j+1))
        S1 = (u(i+1,j)-2*u(i,j)+u(i-1,j))/((delta_r)^2);
        S2 = (u(i+1,j)-u(i,j))/(delta_r);
        u(i,j+1) = u(i,j) + delta_t*(A0 + A1*cos(omega*t) + Beta1*((S1) + 1/r * (S2)));
        disp(u(i,j+1))
        S1n = (u(n+1,j)-2*u(n,j)+u(n-1,j))/((delta_r)^2);
        S2n = (u(n+1,j)-u(n,j))/(delta_r);
        u(n,j+1) = u(n,j) + delta_t*(A0 + A1*cos(omega*t) + Beta1*((S1n) + 1/r * (S2n)));
        disp(u(n,j+1))
    end
end
%Graphical representation of the velocity at different selected times
plot(u, '-', 'LineWidth', 2);
grid on;
fontSize = 16;
xlabel('space', 'FontSize', fontSize)
ylabel('u', 'FontSize', fontSize)