Error using feval Function to evaluate must be represented as a string scalar, character vector, or function_handle object.

% Example5_5.m
% Solution to Example 5.5. This program calculates and plots
% the concentration of cell mass, concentration of penicillin,
% optimal temperature profile, and adjoint variable of a batch
% penicillin fermentor.  It uses the function COLLOCATION to 
% solve the set of system and adjoint equations.
clear
clc
clf
% Input data
w = input(' Enter w''s as a vector : ');
y0 = input(' Vector of known initial conditions = ');
yf = input(' Vector of final conditions = ');
guess = input(' Vector of guessed initial conditions = ');
fname = input('\n M-file containing the set of differential equations : ');
fth = input(' M-file containing the necessary condition function : ');
n = input(' Number of internal collocation points = ');
rho = input(' Relaxation factor = ');
% Solution of the set of differential equations
[t,y] = collocation(fname,0,1,y0,yf,guess,n,rho,[],w,fth);
% Temperature changes
for k = 1:n+2
    options=optimset;
    theta(k) = fzero(fth,30,options,y(:,k),w);
end
% Plotting the results
subplot(2,2,1), plot(t,y(1,:))
xlabel('Time')
ylabel('Cell')
title('(a)')
subplot(2,2,2), plot(t,y(2,:))
xlabel('Time')
ylabel('Penicillin')
title('(b)')
subplot(2,2,3), plot(t,y(3,:))
xlabel('Time')
ylabel('First Adjoint')
title('(c)')
subplot(2,2,4), plot(t,theta)
xlabel('Time')
ylabel('Temperature (deg C)')
title('(d)')


function f = Ex5_5_func(t,y,w,fth)
% Function Ex5_5_func.M
% This function introduces the set of ordinary differential
% equations used in Example 5.5.
% Temperature
options=optimset;
theta = fzero(fth,30,options,y,w);
% Calculating the b's
b1 = w(1) * (1-w(2)*(theta-w(3))^2) / (1-w(2)*(25-w(3))^2);
if b1<0, b1=0; end
b2 = w(4) * (1-w(2)*(theta-w(3))^2) / (1-w(2)*(25-w(3))^2);
if b2<0, b2=1e-6; end
b3 = w(5) * (1-w(2)*(theta-w(6))^2) / (1-w(2)*(25-w(6))^2);
if b3<0, b3=0; end
% Evaluating the function values
f(1) = b1*y(1) - b1/b2*y(1)^2;
f(2) = b3*y(1);
f(3) = -b1*y(3) + 2*b1/b2*y(1)*y(3) - b3;
f = f';	% Make it a column vector



function ftheta = Ex5_5_theta(theta,y,w)
% Function Ex5_5_theta.M
% This function calculates the value of the necessary condition
% as a function of the temperature (theta). It is used in solving
% Example 5.5.
% Calculating the b's
b1 = w(1) * (1-w(2)*(theta-w(3))^2) / (1-w(2)*(25-w(3))^2);
db1 = w(1)*(-w(2))*2*(theta-w(3)) / (1-w(2)*(25-w(3))^2);
b2 = w(4) * (1-w(2)*(theta-w(3))^2) / (1-w(2)*(25-w(3))^2);
db2 = w(4)*(-w(2))*2*(theta-w(3)) / (1-w(2)*(25-w(3))^2);
b3 = w(5) * (1-w(2)*(theta-w(6))^2) / (1-w(2)*(25-w(6))^2);
db3 = w(5)*(-w(2))*2*(theta-w(6)) / (1-w(2)*(25-w(6))^2);
% The function
ftheta = y(3)*(y(1)*db1-y(1)^2*(db1*b2-db2*b1)/b2^2)+y(1)*db3;


function [x,y] = collocation(ODEfile,x0,xf,y0,yf,guess,n,rho,tol,varargin)
%COLLOCATION Solves a boundary value set of ordinary differential
% equations by the orthogonal collocation method.
%
%   [X,Y]=COLLOCATION('F',X0,XF,Y0,YF,GAMMA,N) integrates the set of
%   ordinary differential equations from X0 to XF by the Nth-degree
%   orthogonal collocation method.  The equations are contained in
%   the M-file F.M.  Y0, YF, and GAMMA are the vectors of initial
%   conditions, final conditions, and starting guesses respectively.
%   The function returns the independent variable in the vector X
%   and the set of dependent variables in the matrix Y.
%	
%   [X,Y]=COLLOCATION('F',X0,XF,Y0,YF,GAMMA,N,RHO,TOL,P1,P2,...)
%   uses relaxation factor RHO and tolerance TOL for convergence
%   test.  Additional parameters P1, P2, ... are passed directly to
%   the function F.  Pass an empty matrix for RHO or TOL to use the
%   default value.
%
%   See also SHOOTING
% (c) N. Mostoufi & A. Constantinides
% January 1, 1999
% Initialization
if nargin < 7 | isempty(n)
    n = 1;
end
if nargin < 8 | isempty(rho)
    rho = 1;
end
if nargin < 9 | isempty(tol)
    tol = 1e-6;
end
y0 = (y0(:).')';			% Make sure it's a column vector
yf = (yf(:).')';			% Make sure it's a column vector
guess = (guess(:).')';	% Make sure it's a column vector
% Checking the number of guesses
if length(yf) ~= length(guess)
    error(' The number of guessed conditions is not equal to the number of final conditions.')
end
r = length(y0);			% Number of initial conditions
m = r + length(yf);		% Number of boundary conditions
% Checking the number of equations
ftest = feval(ODEfile,x0,[y0 ; guess],varargin{:});
if length(ftest) ~= m
    error(' The number of equations is not equal to the number of boundary conditions.')
end
fprintf('\n Integrating. Please wait.\n\n')
% Coefficients of the Legendre polynomial
for k = 0 : n/2
    cl(2*k+1) = (-1)^k * gamma(2*n-2*k+1) / ...
        (2^n * gamma(k+1) * gamma(n-k+1) * gamma(n-2*k+1));
    if k < n/2
        cl(2*k+2) = 0;
    end
end
zl = roots(cl);				% Roots of the Legendre polynomial
z = [-1; sort(zl); 1];		% Collocation points (z)
x = (xf-x0)*z/2+(xf+x0)/2;	% Collocation points (x)
% Bulding the vector of starting values of the dependent variables
[p,q] = RK(ODEfile,x0,xf,(xf-x0)/20,[y0 ; guess],2,varargin{:});
for k = 1:m
    y(k,:) = spline(p,q(k,:),x');
end
y(r+1:m,end) = yf(1:m-r);
% Building the matrix A
Q(:,1) = ones(n+2,1);
C(:,1) = zeros(n+2,1);
for i = 1:n+1
    Q(:,i+1) = x.^i;
    C(:,i+1) = i*x.^(i-1);
end
A = C*inv(Q);
for k = 1:m
    k1 = (k-1)*(n+2)+1;
    k2 = k1 + n+1;
    Am(k1:k2,k1:k2) = A;		% Building the matrix Am
    Y(k1:k2) = y(k,:);		% Building the vector Y
end
Y = Y';							% Make it a column vector
Y1 = Y * 1.1;
iter = 0;
maxiter = 100;
F = zeros(m*(n+2),1);
Fa = zeros(m*(n+2),1);
dY = zeros(m*(n+2),1);
position = [];	% Collocation points excluding boundary conditions
for k = 1:m
    if k <= r
        position = [position, (k-1)*(n+2)+[2:n+2] ];
    else
        position = [position, (k-1)*(n+2)+[1:n+1] ];
    end
end
% Newton's method
while max(abs(Y1 - Y)) > tol & iter < maxiter
    iter = iter + 1;
    fprintf(' Iteration %3d\n',iter)
    Y1 = Y;
    % Building the vector F
    for k = 1:n+2
        F(k : n+2 : (m-1)*(n+2)+k) = ...
            feval(ODEfile,x(k),Y(k : n+2 : (m-1)*(n+2)+k),varargin{:});
    end
    fnk = Am * Y - F;
    
    % Set dY for derivation
    for k = 1:m*(n+1)
        if Y(position(k)) ~= 0
            dY(position(k)) = Y(position(k)) / 100;
        else
            dY(position(k)) = 0.01;
        end
    end
    
    % Calculation of the Jacobian matrix
    for k = 1:m
        for kk = 1:n+1
            a = Y;
            nc = (k-1)*(n+1)+kk;
            a(position(nc)) = Y(position(nc)) + dY(position(nc));
            for kkk = 1:n+2
                Fa(kkk : n+2 : (m-1)*(n+2)+kkk) = ...
                    feval(ODEfile,x(kkk),a(kkk:n+2:(m-1)*(n+2)+kkk),varargin{:});
            end
            fnka = Am * a - Fa;
            jacob(:,nc) = (fnka(position) - fnk(position))...
                / dY(position(nc));
        end
    end
    % Next approximation of the roots
    if det(jacob) == 0
        Y(position) = Y(position) + max([abs(dY(position)); 1.1*tol]);
    else
        Y(position) = Y(position) - rho * inv(jacob) * fnk(position);
    end
end
% Rearranging the y's
for k = 1:m
    k1 = (k-1)*(n+2)+1;
    k2 = k1 + n+1;
    y(k,:) = Y(k1:k2)';
end
x = x';
if iter >= maxiter
    disp('Warning : Maximum iterations reached.')
end

[Voss]

Use the 's' (or "s") option in input() in order to store the result as text without evaluating it:

fname = input('\n M-file containing the set of differential equations : ', 's');

fth = input(' M-file containing the necessary condition function : ', 's');

With the 's', fname and fth would be character vectors containing the names of the files you entered (presumably m-file functions) which can then be evaluated using feval, etc.

Without the 's', input() attempts to evaluate the entered text and store the results returned, so your fname and fth variables contain the results of executing (with no inputs and one output) the functions whose names you entered. Evidently the function you entered for fname returns something that's not feval-able (e.g., a numeric matrix), and that's why you get the error when you try to feval it.

From the input documentation, "txt = input(prompt,"s") returns the entered text, without evaluating the input as an expression."

[erfan]

Error using feval

Invalid function name '' after that give this error.

[Voss]

You would have to enter something when prompted for input. What did you enter?

[erfan]

Enter w's as a vector : [13.1, 0.005, 30, 0.94, 1.71, 20]

Vector of known initial conditions = [0.03 , 0]

Vector of final conditions = 0

Vector of guessed initial conditions = 3

M-file containing the set of differential equations : run('C:\Users\cferf\OneDrive\Desktop\Files\پروژه تحقیقاتی\Ex5_5_func.m')

M-file containing the necessary condition function : run('C:\Users\cferf\OneDrive\Desktop\Files\پروژه تحقیقاتی\Ex5_5_theta.m')

Number of internal collocation points = 10

Relaxation factor = 0.9

[erfan]

inputs

Answer 1

[Steven Lord]

Run this command in your MATLAB Command Window. At the prompt, type the five characters bench and press Enter.

fname = input('\n M-file containing the set of differential equations : ')

Once the bench function has finished executing, note that your variable fname does not contain the text 'bench'. It is instead a 1-by-6 double array containing the output from that call to bench. If you want fname to contain the text 'bench' add 's' as the second input argument in your input call.

fname = input('\n M-file containing the set of differential equations : ', 's')

See the input documentation page for more information.

[erfan]

Error using feval

Invalid function name '' after that give this error.

[Steven Lord]

From your comment on Voss's answer, you entered the following at the prompt:

M-file containing the set of differential equations : run('C:\Users\cferf\OneDrive\Desktop\Files\پروژه تحقیقاتی\Ex5_5_func.m')

From how the code you're using calls it, you cannot specify that you want it to call run and run a function in a different location not accessible to MATLAB. What you enter must be the name of a function; no path information allowed.

You would need to cd to that directory before running the code that calls input, add the directory contaiing the file you want to run to the MATLAB search path, or move that function that you're trying to call into the current directory or a directory on the MATLAB search path (you could put it in the directory whose name is returned by the userpath function, for example.)

[erfan]

Unrecognized function or variable 'RK'. fix that and than give this error.

[erfan]

please help

[erfan]

Unrecognized function or variable 'RK'. line(67)

[Steven Lord]

There's no function named RK in MATLAB, nor does it appear to be defined in the code you posted. You should ask whoever gave you the collocation.m file to give you that RK function. Given that this is (base on the copyright line) an over 25 year old file, it's possible they may not have it. In that case you may need to ask (or determine on your own) what that RK function does and the meaning of the input arguments and replace it.

Based on the name I'm guessing you could probably modify that call to be a call to one of the ODE solvers included in MATLAB, but it wouldn't be as simple as erasing the word RK and replacing it with the word ode45.