MATLAB: Log graphic and matrix problem

loggraphMATLAB

hi, i got issue with my code, i want to display function on graph with semilogx but i got "matrix error":

Error using ^ (line 51)

Incorrect dimensions for raising a matrix to a

power. Check that the matrix is square and the

power is a scalar. To perform elementwise matrix

powers, use '.^'.

Error in Grzesik_cz3/plot_g (line 13)

y=20*log(abs((1/(R1*R2*C1*C2))/(((1j*2*pi*x)^2)+((1j*2*pi*x)*((1/(R1*C1))+(1/(R2*C1))+(1/(R2*C2))))+(1/(R1*R2*C1*C2)))));

Error in Grzesik_cz3 (line 9)

plot_g(C1,R1,C2,R2)

thisis my code:

function Grzesik_cz3

%deklaracje

C1=0.000000032;%F%

C2=0.000000032;%F%

R1=1000;%Ohm%

R2=1000;%Ohm%

plot_g(C1,R1,C2,R2)

function plot_g(C1,R1,C2,R2)

x=0.001:1000000;

y=20*log(abs((1/(R1*R2*C1*C2))/(((1j*2*pi*x)^2)+((1j*2*pi*x)*((1/(R1*C1))+(1/(R2*C1))+(1/(R2*C2))))+(1/(R1*R2*C1*C2)))));

figure

semilogx(x,y);

hold off

end

Best Answer

Try with (element wise operation)

.^

Related Solutions

MATLAB: Error running for loop

if true
  syms P
l=100; a=50; b=20;  h0=50; E=200; h1=50;%n=1.5;
for n=1:0.02:4
I0=b*h0^3/12; I1=b*h1^3/12;
L0=sqrt(P/(E*I0-P*n));%L0=simplify(L00);
L1=sqrt(P/(E*I1-P*n));%L1=simplify(L11);
v=0.3;
s=0.5; 
f=1.93-3.07*s+14.53*s^2-25.11*s^3+25.8*s^4;
k=(E*I1)/(6*pi*h1*f*(1-v^2)); 
a11=cos(L1*l) - cos(L1*a) - L1*a*sin(L1*l) + L1*l*sin(L1*l);
a12=sin(L1*l) - sin(L1*a) + L1*a*cos(L1*l) - L1*l*cos(L1*l);
a13=cos(L0*a) - 1;
a14=sin(L0*a) - L0*a;
a21=-(L1*sin(L1*a) - L1*sin(L1*l)) - L1^2*cos(L1*a)*((P*n - E*I1)/k);
a22=(L1*cos(L1*a) - L1*cos(L1*l)) - L1^2*sin(L1*a)*((P*n - E*I1)/k);
a23=L0*sin(L0*a);
a24=(L0 - L0*cos(L0*a));
a31=-L1^2*cos(L1*a)*(P*n - E*I1);
a32=-L1^2*sin(L1*a)*(P*n - E*I1);
a33=L0^2*cos(L0*a)*(P*n - E*I0);
a34=L0^2*sin(L0*a)*(P*n - E*I0);
a41=L1^3*sin(L1*a)*(P*n - E*I1);
a42=-L1^3*cos(L1*a)*(P*n - E*I1);
a43=-L0^3*sin(L0*a)*(P*n - E*I0);
a44=L0^3*cos(L0*a)*(P*n - E*I0);
A=[a11 a12 a13 a14;a21 a22 a23 a24;a31 a32 a33 a34;a41 a42 a43 a44];
delta1=det(A);
delta2=subs(delta1);
delta=simplify(delta2);
F=matlabFunction(delta);
%FF=fplot(F)
%P=vpasolve(delta,P,1e3)
P1=[];
for j = 0.01:10
  PP = fzero(F, j);
  P1 = [P1; PP];
end
P_cr = min(P1(P1 > 0));
D=plot(n,P_cr,'k.','linewidth',1.5);
%axis([0 4 0 1e6])
DD=double(D);
hold on
end
end

MATLAB: Is the script not working

I try

1) I think you are caluclating the jacobian matrix. To avoid mistakes I did this symbolically and the result is

>> syms r1 r2 r3 r4 r5 r6 t1 t2 t3 t4 t5 t6
>> f = [r2*cos(t2)-r3*cos(t3)+r1; r2*sin(t2)-r3*sin(t3); r6-r4*cos(t4)+r1; r5-r4*sin(t4); t4-t3]
 
f =
 
 r1 + r2*cos(t2) - r3*cos(t3)
      r2*sin(t2) - r3*sin(t3)
         r1 + r6 - r4*cos(t4)
              r5 - r4*sin(t4)
                      t4 - t3
 
>> A = jacobian(f,[r3 r4 r5 t3 t4])
 
A =
 
[ -cos(t3),        0, 0,  r3*sin(t3),           0]
[ -sin(t3),        0, 0, -r3*cos(t3),           0]
[        0, -cos(t4), 0,           0,  r4*sin(t4)]
[        0, -sin(t4), 1,           0, -r4*cos(t4)]
[        0,        0, 0,          -1,           1]

It seems that you have different signs in your variable dfdt3

2) you load your derivatives in the matrix columns. It seems to me you are working with the transpose Jacobian.

3) Never ever use inv(A)*f but rather use matrix solution A\f

All in all, I modified your code as follows

clear all; clc;
pi=4.0*atan(1.0);
%scalar knowns
r1=4.8;
r2=2.0;
r6=3.63;
t1=-pi;
t5=-pi/2;
t6=0;
%input theta 2
t2= 283*pi/180;
%guess values of scalar unknowns
r3=3.0;
r4=11.0;
r5=4.0;
t3=5.236;
t4=5.236;
%vector containing initial guesses:
x0=[r3;r4;r5;t3;t4];
x=[0;0;0;0;0];
% counter to limit iterations
counter = 0;
counterLimit = 1e3;
while abs(x-x0) >= 1e-2
    counter = counter+1;
    
    ct2=cos(t2);
    st2=sin(t2);
    ct3=cos(t3);
    st3=sin(t3);
    ct4=cos(t4);
    st4=sin(t4);
    
    %compute functions at current guessed values
    f1=r2*ct2-r3*ct3+r1;
    f2=r2*st2-r3*st3;
    f3=r6-r4*ct4+r1;
    f4=-r5-r4*st4;
    f5=t4-t3;
    
    %define vector for computed functions of guessed values
    f=[f1;f2;f3;f4;f5];
    
    %calculate partial derivatives of f w.r.t. each element of x
    dfdr3=[-ct3; 0; 0; r3*st3; 0];
    dfdr4=[-st3; 0; 0; -r3*ct3; 0];
    dfdr5=[0; -ct4; 0; 0; r4*st4];
    dfdt3=[0; -st4; 1; 0; -r4*ct4];
    dfdt4=[0; 0; 0; -1; 1];
    
    % Define the A matrix
    A= [dfdr3 dfdr4 dfdr5 dfdt3 dfdt4];
    
    %use equation (2.67) to compute the solution x
    x=-A.'\f+x0;
    r3=x(1);
    r4=x(2);
    r5=x(3);
    t3=x(4);
    t4=x(5);
end
if counter == counterLimit
    warning('Failed')
end
fprintf(' %f\n', x);

This code does provide a solution, if it is correct is up to you.

As a side note, I think it should be better coding not to use r1 r2 r3 r4 r5 r6 t1 t2 t3 t4 t5 t6 as variables, but I would rather use the vector x, and accessing with indexing (x(1), x(2), ...)

Best Answer

Related Solutions

MATLAB: Error running for loop

MATLAB: Is the script not working

Related Question