How to store values in a matrix?

Hello. I am trying to store my theta and E values in a matrix to be able to plot them. This is what I have done so far but it does not work. I would appreciate some help. Thank you so much!

clear all
close all 
clc

[separated off so if somebdody downloads won't wipe their workspace accidentally -- dpb]

% define degree increments of 5 from 0 to 90 
theta = 0:5:90;
%given information 
Eone = 1.54*10^11;
Etwo = 8.96*10^9;
Ethree = Etwo;
Vonetwo = 0.32;
Vonethree = Vonetwo;
Vtwothree = 0.5;
Gonetwo = 5.32*10^9;
Gonethree = Gonetwo;
Gtwothree = 2.99*10^9;
% S matrix 
S = [(1/Eone) (-Vonetwo/Eone) (-Vonethree/Eone) 0 0 0; 
    (-Vonetwo/Eone) (-1/Eone) (-Vtwothree/Etwo) 0 0 0 ; 
    (-Vonethree/Ethree) (-Vtwothree/Ethree) (1/Ethree) 0 0 0;
    0 0 0 (1/Gonetwo) 0 0 ; 0 0 0 0 (1/Gonethree) 0; 
    0 0 0 0 0 (1/Gtwothree)];
syms sigma [3 3]
sigma ;
sigmaprime = [ 1 0 0 ; 0 0 0 ; 0 0 0 ] ;
%define the rotating matrix for theta from 0 to 90 degrees in increments
%of 5
for theta = 0:5:90
    R = [cos(theta) (-sin(theta)) 0; sin(theta) cos(theta) 0; 0 0 1];
end
%get sigm prime 
Rt= R.';
sigma = Rt * sigmaprime * R;
%sigma as 1 by 6 
newsigma = [ 0.2008; 0.4006 ;0; 0.4006; 0.7992; 0];
%get epsilon by sigms times S
epsilon = newsigma .* S;
%epsilon as 3 by 3 
newepsilon  = [ 0.0013 -0.0004 -0.0004; -0.0008 -0.0026 -0.0224; 0 0 0];
%find epsilon prime 
epsilonprime = R * newepsilon * Rt;
%solve for modulus E by epsilon'(1,1)/sigma'(1,1)
E = epsilonprime(1,1)/newsigma(1,1)
%plot 
E = zeros(19,1)
theta = zeros(19,1)
plot(theta,E)
xlabel('θ = Degrees')
ylabel('Modulus of the material as a function of θ (Pa)')
title('Exx Modulus')

[Sharmin Kibria]

You are trying to plot theta and E, right? It seems like you are setting both theta and E to zero on the line just before plot. When you are calling the plot function, it is plotting only the (0,0) value. That is why you don't see the desired plot. Whateevre calculations you have done gets overwritten by the E = zeros(19,1)

theta = zeros(19,1) command.

I hope it helps.

Answer 1

[Walter Roberson]

for theta = 0:5:90
  R = [cos(theta) (-sin(theta)) 0; sin(theta) cos(theta) 0; 0 0 1];
end

That is not creating one R for each different theta, it is overwriting R each time.

You do matrix multiplication by R or R' so you cannot simply make R into a 3d matrix. You could potentially recode using pagemtimes() calls if you made R into 3d.

Or perhaps you should make theta a symbolic scalar and carry it through until afterwards you subs in a vector of values.

Oh, and be careful, you are taking sin of 5 to 90 radians not degrees.