Inputing a function into another function: left and right sides have different elements

I am quite new to matlab, so hopefully someone can spot my errors!

I have a water function that depends on pressure. The pressure is given a function that changes with time (called Pressure_function). The coefficients are stored in an array called c. This is the pressure function:

function p = Pressure_function(t,c)
 
p = c(:,1)*t.^8 + c(:,2)*t.^7 + c(:,3)*t.^6 + c(:,4)*t.^5 + c(:,5)*t.^4 + c(:,6)*t.^3 + c(:,7)*t.^2 + c(:,8)*t + c(:,9);

p = p*10^5; %convert to [Pa]

end 

Now, I have the water function (which is based off a CSTR in series model at steady state). When the pressure is constant, the function works perfectly. However, I want to make this function transient by inputting the pressure function, since it changes with time. I thougt this would be relatively straightforward (see below). However, I continue to end up with the error 'left and right side have different elements'. I'm not sure how to fix this, so any help would be appreciated!

function [vw] = Water_ss_func(t, ps)
p = @Pressure_function;

%Preallocate (ps.nr is the number of CSTR in series - stored in my struct)
vw = zeros(1,ps.nr);

vw(1) = ps.fv_in - (ps.k *ps.area * p(t,c))/ps.c_w;

for i = 2:ps.nr
    vw(i) = vw(i-1) - (ps.k *ps.area * p(t,c))/ps.c_w;
end

end     

[Sudhakar Shinde]

Can you add 't' and 'ps' inputs here so that we can pass this and check it.

[Stephen23]

Where is c defined? What sizes and classes do the input data have?

I suspect that all of the mtimes * in the function should actually be times .*

https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

[isabella Anglin]

Yes, of course, here are my ps values:

%Create parameter structs
ps = struct; 
ps.nr = 44; %number of CSTRs
ps.fv_in = 20 * (10^-3)/3600; %[l/hr] converted to [m3/s]
ps.v_in = 20 * 55.85/3600; %[l/hr] to [mol/s]
ps.k = 0.000005; %inital guess
ps.area = 0.08/ps.nr; %Area of each CSTR for permeation [m2]
ps.p_ext = 2.2864 *10^5; %barg converted to pascal [Pa] 
ps.c_bsa_in = 0.0323; %mol/m3 (taken from steady state value of feed
ps.R = 8.314; %J/molK
ps.vol = (0.00083^2 *pi/4 * 102 *0.30)/ps.nr;
ps.T = 298; %K
ps.c_w = 55358; %[mol/m3] of water 
ps.nw_in = ps.vol *ps.c_w; %[mol] water

And c is:

c = 3.96579976144065e-16	7.69738447503576e-14	-1.30016421641611e-10	3.89802375870541e-08	-5.57066417121402e-06	0.000438052477869725	-0.0190876028666973	0.412616772886201	-0.564804289797713

And the time input will be t_exp, the experimental time, from 0 to 146.2 s (see attached mat file!)

Thank you in advance for your help :)

[Uday Pradhan]

Hi Isabella,

Since t_exp is a 145 x 1 vector, the line:

vw(1) = ps.fv_in - (ps.k *ps.area * p(t,c))/ps.c_w;

is causing an error as the sizes of the two sides are not the same. p(t_exp,c) will also return a 145 x 1 vector and we cannot assign this to vw(1) since it's a scalar. May be you want to evaluate Water_ss_func at each time step? Something like:

Water_ss_func(t_exp(10), ps)