Error witth Matrix calculus

Hi all,

I am trying to calculate such a system:

For which I already know the solution:

But when I put all this stuff into Matlab, I get the following error:

    >> syms L C R s;
    >> C = [[R + s*L,-s*L];[-s*L, R + s*L + 1/(s*C)]]

    C =

    [ R + L*s,              -L*s]
    [    -L*s, R + L*s + 1/(C*s)]
    >>V = [[R + s*L,1];[-s*L,0]]

    V =

    [ R + L*s, 1]
    [    -L*s, 0]
    >> i2 = det(V)/det(C)

    ans =

    (C*L*s^2)/(C*R^2*s + 2*C*L*R*s^2 + R + L*s)

    >> vo = i2/(s*C)
    Error using symengine (line 59)
    Operands are invalid.

    Error in sym/privBinaryOp (line 903)
                Csym = mupadmex(op,args{1}.s, args{2}.s, varargin{:});

    Error in  /  (line 297)
            X = privBinaryOp(A, B, 'symobj::mrdivide');

Why Matlab cannot perform such a calculation ? This is not the first time I perform these kind of calculations.

Instead, If I declare a variable C1, it all works:

>> syms C1
>> C = [[(R + s*L),-s*L];[-s*L, (R + s*L + 1/(s*C1))]]

C =

[ R + L*s,               -L*s]
[    -L*s, R + L*s + 1/(C1*s)]

>> V = [[R + s*L,1];[-s*L,0]]

V =

[ R + L*s, 1]
[    -L*s, 0]

>> i2 = det(V)/det(C)/(s*C1)

i2 =

(L*s)/(C1*R^2*s + 2*C1*L*R*s^2 + R + L*s)

What's the problem with variable named C ? Thank you for yor help.

Answer 1

[John D'Errico]

The problem is NOT the name of the variable C, but what it contains and what you are doing.

LOOK at the line that had trouble.

vo = i2/(s*C)

i2 and s are scalars. C is a 2x2 matrix.

What do you expect matlab to do when you try to divide by a 2x2 matrix?

[John D'Errico]

Moved an answer to a comment by @zmath

"Ooops I did not realize I mixed matrix name and variable. I am feeling quiet stupid right now. Put this on the top 10 of MSQ. Bye."

Answer 2

[arvind thakur]

I have an error like below,

Error using plot

Data must be numeric, datetime, duration or an array convertible to double.

Error in pressuremodel (line 36)

plot(a,K1,'.-b');

my code is:

%% pressure at crack wake due to bridgindg after application of remote stress
clc
close all
clear
a=0.001:0.0002:0.0018;
syms x a w
%x=1.0:0.1:1.98;
Ef=427000*10^6; % in Pa
Em=89000*10^6;
Ec=184000*10^6;
%mu=0.2825;
%v=0.36;
ao=0.001;
w=0.00512;
%R=.0725;
S=198*10^6;
%tow=20;
m1=0.6147+17.1844*(a.^2./w^2)+8.7822*(a.^6./w^6);
m2=0.2502+3.2889*(a.^2./w^2)+70.0444*(a.^6./w^6);
H=(1+m1*((a-x)./a)+m2*((a-x)./a).^2);
c=S*((w./(w-ao))+6*w*ao*((0.5*(w-ao)-(x-ao))./(w-ao)^3));
j=int((S*H)./(sqrt(a-x)), [0 ao]);
L=int(((S-c)*H)./(sqrt(a-x)), [ao a]);
K=sqrt(2/3.14)*(j+L);
K1=((K*(Em./(Ec)))./10^7);





plot(a,K1,'.-b');

help can appreciated in advance.

[John D'Errico]

PLEASE DON'T post a completely new question as an answer. This is NOT an answer to that question, and your problem is not even remotely the same. Repost the question AS a question on Answers. I'll delete this answer soon.