is the "for loop" is wrong? what can be the solution?

clc

ti = 0;

tf = 100E-4;

tspan=[ti tf];

o = 1E6;

tc = 70E-9;

tf = 240E-6;

a1 = 0.02;

a2 = 0.02;

P1 = 1;

P2 = 1;

k = 0.033;

l = 0.5;

f = @(t,y) [ ((y(2)-a1).*y(1)) + k.*(y(1).*cos(y(3))).*(2/tc);

(P1 - y(2).*(1+y(1)))./tf;

o - (k / tc) * 2 * sin(y(3));

];

[T,Y] = ode45(f,tspan,[1;1;0].*10E-3);

% this is the for loop, maybe this is wrong

Y(:,3) = -3:0.01:3;

U = zeros(length(k),1) ;

for i = 1:length(k)

U(i) = -o.*(Y(:,3)) - 2.*(k./tc).*cos(Y(:,3) - pi/2)

end

%plotting the graphs

plot(T,Y(:,3));

xlim([0 10E-5])

xlabel('t')

ylabel('phase difference')

legend('k = 0.033')

plot(Y(:,3),U)

[Abderrahim. B]

Hi!

The below lines of code are not correct. Read the comments below and try to rereview your code, and maybe you share what you are trying to do with this for loop.

Y(:,3) = -3:0.01:3; % this assignement is not correct size(-3:0.01:3) is different from size(Y(:,3))
U = zeros(length(k),1) ; % k is a scalar thus U is a scalar

for i = 1:length(k) % length(k) is one >> one iteratio, what is the point to use a for loop!!
     U(i) = -o.*(Y(:,3)) - 2.*(k./tc).*cos(Y(:,3) - pi/2) % This assignment is not possible size(U(i)) does not match the size of the right side.
end

[SAHIL SAHOO]

I calculated the Y(:,3) which represent Φ, i want to calculate the U for different value of Φ, where the U is

then I want to plot (Y(:,3), Φ)

[Abderrahim. B]

Okay now is clear what you re trying to do. You do not need a loop. One of MATLAB advantages is vectorization. Check out @Torsten answer.

[VBBV]

You can also use for loop as shown in your code. But plot you mentioned plot (Y(:,3), Φ) is strange. It will be a straight line since Y(:,3) and Φ are same according to your equation and code written. Do you mean plot (Y(:,3), U) ?

[VBBV]

The for loop code works well as shown in my answer below. which can also be done without a loop.

[SAHIL SAHOO]

yeah I mean plot (Y(:,3), U) and the graph is correct too.

Answer 1

[VBBV]

clc
ti = 0; 
tf = 100E-4;
tspan=[ti tf];
o = 1E6;  
tc = 70E-9; 
tf = 240E-6;  
a1 = 0.02;
a2 = 0.02;
P1 = 1;
P2 = 1;
k = 0.033; 
l = 0.5;
f = @(t,y) [ ((y(2)-a1).*y(1)) + k.*(y(1).*cos(y(3))).*(2/tc);
            
                (P1 - y(2).*(1+y(1)))./tf;
                             
                  o - (k / tc) * 2 * sin(y(3));                       
                 
                 ];
[T,Y] = ode45(f,tspan,[1;1;0].*10E-3);
 % this is the for loop, maybe this is wrong  ... yes this assignment is
 % incorrect 
Y(:,3) = linspace(-3,3,length(Y));  % change this 
U = zeros(length(Y),1) ; 
for i = 1:length(Y)
     U(i) = -o.*(Y(i,3)) - 2.*(k./tc).*cos(Y(i,3) - pi/2);   % also this
end
%plotting the graphs
figure(1)
plot(T,Y(:,2));

figure(2)
plot(T,U)
xlim([0 10E-5])
xlabel('t')
ylabel('phase difference')
legend('','k = 0.033')

Warning: Ignoring extra legend entries.

plot(T,U)

You can plot both U and T variables , but for loop needs modififcation

[VBBV]

clc
ti = 0; 
tf = 100E-4;
tspan=[ti tf];
o = 1E6;  
tc = 70E-9; 
tf = 240E-6;  
a1 = 0.02;
a2 = 0.02;
P1 = 1;
P2 = 1;
k = 0.033; 
l = 0.5;
f = @(t,y) [ ((y(2)-a1).*y(1)) + k.*(y(1).*cos(y(3))).*(2/tc);
            
                (P1 - y(2).*(1+y(1)))./tf;
                             
                  o - (k / tc) * 2 * sin(y(3));                       
                 
                 ];
[T,Y] = ode45(f,tspan,[1;1;0].*10E-3);
 % this is the for loop, maybe this is wrong  ... yes this assignment is
 % incorrect 
Y(:,3) = linspace(-3,3,length(Y));  % change this 
U = zeros(length(Y),1) ; 
for i = 1:length(Y)
     U(i) = -o.*(Y(i,3)) - 2.*(k./tc).*cos(Y(i,3) - pi/2);   % also this
end
%plotting the graphs
figure(1)
plot(Y(:,3),U);  % i guess you are looking for this 

i guess you are looking for this

[SAHIL SAHOO]

yes, this graph is correct that what i expected, without for loop I get a straight line.

Answer 2

[Torsten]

ti = 0; 
tf = 100E-4;
tspan=[ti tf];
o = 1E6;  
tc = 70E-9; 
tf = 240E-6;  
a1 = 0.02;
a2 = 0.02;
P1 = 1;
P2 = 1;
k = 0.033; 
l = 0.5;
f = @(t,y) [ ((y(2)-a1).*y(1)) + k.*(y(1).*cos(y(3))).*(2/tc);
    
(P1 - y(2).*(1+y(1)))./tf;

o - (k / tc) * 2 * sin(y(3));                       

];
[T,Y] = ode45(f,tspan,[1;1;0].*10E-3);
% this is the for loop, maybe this is wrong
U = -o.*Y(:,3) - 2.*(k./tc).*cos(Y(:,3) - pi/2);
%plotting the graphs
plot(T,Y(:,3));
xlim([0 10E-5])
xlabel('t')
ylabel('phase difference')
legend('k = 0.033')

plot(Y(:,3),U)