using loops and arrays to solve for variables in equations

Hi I am new to matlab and am trying to become more familiar with using arrays and loops to solve for variables in equations. The goal of this script is to create an array of values for the variables 'x' and 'vis' (viscosity). I know I am not doing somethings quite right. The end result in my workspace are 0x0 matrices for epsUse, x, and vis. The loop I created for temperature (Texplore/Tuse) only seems to use one value instead of all 5. Early in the script I designate epsUse=1e-14 and later on I set the %flow law equation=epsUse to attempt to solve for the variable x. Any tips/direction/help would be appreciated!

clc

clear

close all

x=zeros(5:1);

vis=zeros(5:1);

%strain rate

epsUse=1e-14;

Puse=1e9;

PARAMS.R=8.314; %ideal gas constant

%dry anorthite flow law parameters

n=3;

A=5e12;

Q=641000;

V=24e-6;

%temperature array

Texplore=[200 400 600 800 1000];

for i=1:length(Texplore)

Tuse=Texplore(i);

%fugacity

fugacity=5521*exp((-31.28*1e3+Puse*20.09e-6)/(PARAMS.R*Tuse));

%correction factor

correctionFACTOR=(3^(n+1))/2;

%flowlaw

epsUse=correctionFACTOR*A*fugacity*x^n*exp((-Q+Puse*V)/(PARAMS.R*Tuse));

%viscosity

vis=x/(2*epsUse);

end

[Steven Lord]

Torsten gave you the corrected code. For an explanation, when you use : to create the size vector for a call to zeros, ones, etc. and you didn't intend to do that, you either get an empty array:

sz = 5:1

sz =

  1x0 empty double row vector

x = zeros(sz)

x =

     []

whatYouProbablyWanted = zeros(5, 1)

whatYouProbablyWanted = 5×1

0 0 0 0 0

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or you may get something much larger than you expected (or an error.)

whatYouWanted = zeros(1,20) % works

whatYouWanted = 1×20

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

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y = zeros(1:20) % does not work

Error using zeros
Requested array exceeds the maximum possible variable size.

That latter line of code and the error tells you you cannot make a 1-by-2-by-3-by-4-by-5-by-6-by-7-by-8-by-9-by-10-by-11-by-12-by-13-by-14-by-15-by-16-by-17-by-18-by-19-by-20 array.

Answer 1

[Torsten]

You mean this ?

x=zeros(5,1);
vis=zeros(5,1);
%strain rate
epsUse=1e-14;
Puse=1e9;
PARAMS.R=8.314; %ideal gas constant
%dry anorthite flow law parameters
n=3;
A=5e12;
Q=641000;
V=24e-6;
%temperature array
Texplore=[200 400 600 800 1000];
for i=1:length(Texplore)
    Tuse=Texplore(i);
    %fugacity
    fugacity=5521*exp((-31.28*1e3+Puse*20.09e-6)/(PARAMS.R*Tuse));
 
    %correction factor
    correctionFACTOR=(3^(n+1))/2;
    %flowlaw
    x(i) = (epsUse/(correctionFACTOR*A*fugacity*exp((-Q+Puse*V)/(PARAMS.R*Tuse))))^(1/n);
    %epsUse=correctionFACTOR*A*fugacity*x^n*exp((-Q+Puse*V)/(PARAMS.R*Tuse));
    %viscosity
    vis(i)=x(i)/(2*epsUse);
end

[Corey]

amazing thank you!