How can I refer to a variable, defined in one .m file, within a function defined in another?

I define a mixed cell in KSP_run.m:

 %%Define celestial body characteristics and scientific constants
           %Body        Eq. Radius   Mass         R. Period   SOI
 bodies = {'The Sun'    2.616e+08    1.757e+28    4.32e+05    Inf          ;
             'Moho'     2.5e+05      1.757e+28    4.32e+05    9.647e+06    ;
             'Eve'      7e+05        1.224e+23    8.046e+04   8.5109e+07   ;
               'Gilly'  1.3e+04      1.242e+17    2.82e+04    1.26e+05     ;
             'Kerbin'   6e+05        5.292e+22    2.1549e+04  8.4159e+07   ;
               'Mun'    2e+05        9.76e+20     1.3896e+05  2.43e+06     ;
               'Minmus' 6e+04        2.646e+19    4.038e+04   2.247e+06    ;
             'Duna'     3.2e+05      4.515e+21    6.546e+04   4.7922e+07   ;
               'Ike'    1.3e+05      2.782+20     6.546e+04   1.05e+06     ;
             'Dres'     1.38e+05     3.219e+20    3.48e+04    3.2833e+07   ;
             'Jool'     6e+06        4.233e+24    3.6e+04     2.445985e+09 ;
               'Laythe' 5e+05        2.94e+22     5.298e+04   3.724e+06    ;
               'Vall'   3e+05        3.109e+21    1.0596e+05  2.306e+06    ;
               'Tylo'   6e+05        4.233e+22    2.1192e+05  1.0857e+07   ;
               'Bop'    6.5e+04      3.726e+19    5.445e+05   1.221e+06    ;
               'Pol'    4.4e+04      1.081e+19    9.0186e+05  1.042e+06    ;
             'Eeloo'    2.1e+05      1.115e+21    1.946e+04   1.19083e+08 };
 G = 6.6741e-11;

I define the function KSP_bod in KSP_bod.m:

 %%Pick a celestial body and define its parameters.
 function [R,M,T,SOI] = KSP_bod()
 body = input('Please enter a celestial body to focus on: ','s');
 row = find(strcmp(bodies,body));
 R = bodies(row,2);
 M = bodies(row,3);
 T = bodies(row,4);
 SOI = bodies(row,5);
 end

KSP_bod.m is called immediately after bodies and G are defined in KSP_run.m:

 [R,M,T,SOI] = KSP_bod();

It seems that KSP_bod.m does not recognise the existence of bodies.The following issue occurs:

 Undefined function or variable 'bodies'.

 Error in *KSP_run* (line 3)
 row = find(strcmp(bodies,body));

 Error in *KSP_run* (line 24)
 [R,M,T,SOI] = KSP_bod();

I believe the issue is scope-related but do not know how to fix it. Referring to bodies outside of KSP_bod.m (e.g. by typing:

 bodies

into the command window) works perfectly fine.

Answer 1

[Fangjun Jiang]

Define it as an input argument and pass the value in

function [R,M,T,SOI] = KSP_bod(bodies)

call using the syntax

[R,M,T,SOI] = KSP_bod(bodies)

[Nicole]

Thanks! This was simple but I couldn't find similar issues online so I never thought of it... the variables R, M, T, SOI are now 1x1 cells. Is this different from a simple number, such as G? Is there a way to be able to just type 'KSP_bod' into the command window and have it work, or is this the only solution to my issue?

[Fangjun Jiang]

Change to this will give you the number (the content of the cell}

R = bodies{row,2};
 M = bodies{row,3};
 T = bodies{row,4};

[Stephen23]

"the variables R, M, T, SOI are now 1x1 cells. Is this different from a simple number, such as G?"

Yes: cell arrays are a container variable, which can contain other arrays.

https://www.mathworks.com/help/matlab/matlab_prog/what-is-a-cell-array.html

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html

"Is there a way to be able to just type 'KSP_bod' into the command window and have it work, or is this the only solution to my issue?"

There are always other ways of doing things... But passing values as input/output arguments, as Fangjun Jiang showed you, is by far the simplest and most efficient way of getting data out of a function.

[Nicole]

Thanks so much! Problem solved plus bonus fix in thirty minutes! Very grateful <3