substituting function variable in function handle

Question

Bathala Teja 2021-9-14

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1452704-substituting-function-variable-in-function-handle

编辑： Jaynik 2024-4-3，10:15

i want to substitute y(5) in place of theta and poceed for the ode calculations.

Here is my script

syms theta
A0 = cos(theta).*[1 5 6; 2 9 3; 1 4 5]; 
A =[A0 zeros(3, 2);
    zeros(2, 3) [1 0; 0 1]]
B = tan(2*theta).*[8 5 1 0 0; 1 1 6 0 0; 2 4 7 0 0; 0 0 0 0 0; 0 0 0 0 0]
C = (cos(2*theta)+2).*[8 5 1; 0 1 6; 2 4 7];
myfun = @(t,y)scriptname(t,y,A,B,C);
% dummy values for tspan and y0
tspan = [0 1];
y0 = zeros(1, 5);
An = matlabFunction(subs(A, y(5)))
Bn = matlabFunction(subs(B, y(5)))
Cn = matlabFunction(subs(C, y(5)))
sol = ode45(myfun,tspan,y0);
h = figure;
plot(sol.x,sol.y(i,:));
function dydt = scriptname(t,y,An,Bn,Cn)
inertia = 0.05;
Wr = 2*pi*50;
p =2;
% Cn = double(subs(C,y(5)))
for i=1:3
    I(i,1)=y(i);
end
I
Te = 1/2*p*I'*Cn*I
if t<0.75
    Tl=0;
else
    Tl=7.31;
end
V = [1.4142*400/sqrt(3)*cos(Wr*t);
    1.4142*400/sqrt(3)*cos(Wr*t+2.*pi/3.);
    1.4142*400/sqrt(3)*cos(Wr*t-2.*pi/3.);
    (Te-Tl)/inertia;
    y(4)]
% An = double(subs(A,y(5)))
% Bn = double(subs(B,y(5)))
dydt = An\V-(Bn*y);
end

It is showing the error of "unrecognized function or variable y".

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Bathala Teja 2021-9-14

sir can you please rewite my script with your changes?

iam really confused sir please help me out

Bathala Teja 2021-9-14

hello

anything edited??

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Answer 1

Jaynik 2024-4-2，11:57

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1452704-substituting-function-variable-in-function-handle#answer_1434941

编辑：Jaynik 2024-4-3，10:15

在 MATLAB Online 中打开

Hi Bathala,

The error you are encountering occurs because "y" is not defined in the scope where you are trying to substitute "y(5)" for "theta" in matrices "A", "B", and "C". To fix this issue, "y" must first be declared as a symbolic variable. that represents a vector, and then perform the substitution.

You can refer to the following code:

syms theta
syms y [5 1]
A0 = cos(theta).*[1 5 6; 2 9 3; 1 4 5]; 
A =[A0 zeros(3, 2); zeros(2, 3) [1 0; 0 1]];
B = tan(2*theta).*[8 5 1 0 0; 1 1 6 0 0; 2 4 7 0 0; 0 0 0 0 0; 0 0 0 0 0];
C = (cos(2*theta)+2).*[8 5 1; 0 1 6; 2 4 7];
% Substitute theta with y(5) in A, B, C
A_sub = subs(A, theta, y(5));
B_sub = subs(B, theta, y(5));
C_sub = subs(C, theta, y(5));
% Convert the substituted expressions to MATLAB functions
An = matlabFunction(A_sub, 'Vars', {y});
Bn = matlabFunction(B_sub, 'Vars', {y});
Cn = matlabFunction(C_sub, 'Vars', {y});
function dydt = scriptname(t, y, An, Bn, Cn)
    inertia = 0.05;
    Wr = 2*pi*50;
    p = 2
    % Using the An, Bn, and Cn functions with the current state vector y
    A_current = An(y);
    B_current = Bn(y);
    C_current = Cn(y);
    
    I = y(1:3);
    Te = 1/2 * p * I' * C_current * I;
    if t < 0.75
        Tl = 0;
    else
        Tl = 7.31;
    end
    V = [1.4142*400/sqrt(3)*cos(Wr*t);
         1.4142*400/sqrt(3)*cos(Wr*t+2*pi/3);
         1.4142*400/sqrt(3)*cos(Wr*t-2*pi/3);
         (Te - Tl) / inertia;
         y(4)];
    dydt = A_current \ V - (B_current * y);
end