variable is not recognized from other function

Unrecognized function or variable 'Mi'.

Error in FourStrokeCycle (line 40)

Mbar=Mi*nin(1)/nin

function [pa,Ta,sa,cpi,Mi,nin] = AirProperties()
AirMatrix= readmatrix('AirProperties.xlsx');
pa=101325
Ta=273
sa=3796

cpi= AirMatrix(3,:)
Mi= AirMatrix(2,:)
nin= AirMatrix(1,:)
end


function [therm,chem,r_c,mfuel,mC02,ddt] = FourStrokeCycle(D,d,rpm,fuel,N)
fuel=0;
fuel= FuelProperties(fuel);
airprop= AirProperties();

%test inputs
rpm=1500
d=.02
N=6

V0=0.00006
L=0.1
D=0.02
PhiI=pi/6
PhiE=pi/6
omega= rpm* 0.10472
% convert rpm to omega rad/s

k=[1:1:N+1]
PhiK=(k-1)*(4*pi)/N
tK=(k-1)*(4*pi)/(N*omega)
PhiT= omega.*tK



x=(D/2)*cos(PhiT)+sqrt(((4*L^2)/D^2)-sin(PhiT).^2)
Vt= V0+(pi.*d^2)./4.*(L+(D./2)-x)
r_c= (V0+D*(pi*d^2)/4)/V0


therm = zeros(8,N+1)


P=zeros(1,N+1)
T=zeros(1,N+1)
P(1)=101325


Ru=8.3145
Mbar=Mi*nin(1)/nin

[Stephen23]

How to call functions with multiple outputs is explained ihere:

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

Answer 1

[Walter Roberson]

function [pa,Ta,sa,cpi,Mi,nin] = AirProperties()

You define AirProperties as returning six separate outputs.

airprop= AirProperties();

When you call AirProperties, you only assign the first output to anything. airprop is going to become that value that was assigned to pa inside AirProperties() .

MATLAB is not going to say, "Oh, there are another 5 outputs, I guess I will assign them to variables with the same name as the names in the output list of the function that was called!" . When you have a potential output and the calling function does not assign it to a variable (or, in the case of the first output, use the value in an expression), then the output is simply discarded

If you want to get at the Mi that was returned by AirProperties() then when you call AirProperties you need to assign it to a variable. For example,

[airprop, ~, ~, ~, Mi, ~] = AirProperties();