# How to call a variable matrix from one script to another script

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Bathala Teja on 7 Sep 2021
Commented: Bathala Teja on 8 Sep 2021
I have two scripts. In first one i will get A and B matrices which are interms of theta as shown below.
sym theta
A = cos(theta).*[1 5 6;
2 9 3;
5 1 0]
B = tan(2*theta).*[8 5 1;
0 1 6;
2 4 7]
I want to use these A and B matrices in another script, which is given below
function dydt = scriptname(t, y)
theta = y(3); % Substitute y(3) in place of theta in A and B matrices
A % Extract A matrix
B % Extract B matrix
V = [1;
5;
3]
dydt = V-((A+B)*Y);
end
Finally i will plot these ODE's in another script that i didnt gave here.
My main doubt is how to extract A and B matrices(especially those are variable matrices) into another script.
After extracting these A and B matrices i will substitute y(3) so that i can get rid of theta.
I havent shown my exact problem because its too complicated. Focus on my main doubt dont care about values.

Fabio Freschi on 7 Sep 2021
I am not sure I have understtod correctly your problem. I give it a try.
I would add an extra layer using an anonymous function to solve the porblem of passing A and B to your funciton
clear variables, close all
% anonymous functions to calculate A and B
A = @(theta)cos(theta).*[1 5 6; 2 9 3; 5 1 0];
B = @(theta)tan(2*theta).*[8 5 1; 0 1 6; 2 4 7];
% extra layer to pass also A and B to your dydt function
myfun = @(t,y)scriptname(t,y,A,B);
% dummy values for tspan and y0
tspan = [0 1];
y0 = [0; 0; 0];
% ode solver
sol = ode45(myfun,tspan,y0);
function dydt = scriptname(t,y,A,B)
theta = y(3); % Substitute y(3) in place of theta in A and B matrices
V = [1; 5; 3];
% actual calculation of A and B with the current value for theta
dydt = V-((A(theta)+B(theta))*y);
end
Bathala Teja on 8 Sep 2021
Ok thank you

### More Answers (1)

Jan on 7 Sep 2021
Edited: Jan on 7 Sep 2021
The first code shows a "script", the second one a "function". While scripts share their variables with the callers automatically, functions don't. As far as I understand all you havt to do is to call the script:
% Script file: "yourScript.m"
sym theta
A = cos(theta).*[1 5 6;
2 9 3;
5 1 0]
B = tan(2*theta).*[8 5 1;
0 1 6;
2 4 7]
% Function file: "scriptname.m" ( missleading name! This is not a script.)
function dydt = scriptname(t, y)
theta = y(3); % Substitute y(3) in place of theta in A and B matrices
yourScript; % <-- A and B are defined internally
V = [1;
5;
3]
dydt = V-((A+B)*Y);
end
For productive code, scripts are a shot in your knee, because you cannot see directly, where the variables are defined. Use functions instead, to forward variables explicitly:
% Script file: "yourFunction.m"
function [A, B] = yourFunction()
sym theta
A = cos(theta).*[1 5 6;
2 9 3;
5 1 0]
B = tan(2*theta).*[8 5 1;
0 1 6;
2 4 7]
end
% Function file: "theOtherFunction.m"
function dydt = theOtherFunction(t, y)
[A, B] = yourFunction();
V = [1;
5;
3]
dydt = V-((A+B)*Y);
end
Bathala Teja on 7 Sep 2021
ok thank you for your explanation

R2021a

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