Symbolic function doesn't work

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John F 2020-12-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/700210-symbolic-function-doesn-t-work

评论： Star Strider 2020-12-22

syms L alpha gamma Y2 Y3 Y4 Y5 Y6 x X dL T(L,x)
syms T(L,x)
M1 = 0;
M2 = 7;
Y1 = 1 + M2 / 10;
Y7 = 3 + M1 / 10;
xcp = [0 0.1*L 0.25*L 0.5*L 0.6*L 0.75*L L];
ycp = [Y1 Y2 Y3 Y4 Y5 Y6 Y7];
T0 = 5 + 1/L - 25/(L^2);
S = bezier_syms();
ode = diff(T,x) == (1+alpha*M1)*(T^2)*S(L,x,Y2,Y3,Y4,Y5,Y6) - 4*(2 + gamma*M2)*x*T;
derivL = diff(ode,L);
U = diff(T,L);
eqns = [derivL, diff(T,L) == dL];
eqns = matlabFunction(eqns);
sol = ode45(eqns,[0 5],diff(T0,L));

I get the error:

Warning: Function 'T' not verified to be a valid MATLAB function.

For some reason it doesn't let me define the T function. Any ideas?

Edit:

function S = bezier_syms()
syms t x y s X Y2 Y3 Y4 Y5 Y6 L
M1 = 0;
M2 = 7;
Y1 = 1 + M2 / 10;
Y7 = 3 + M1 / 10;
xcp = [0 0.1*L 0.25*L 0.5*L 0.6*L 0.75*L L];
ycp = [Y1 Y2 Y3 Y4 Y5 Y6 Y7];
N = length(xcp) - 1;
% Calculate m matrix
m = zeros(N+1,N+1);
for i=0:N
    for j=0:N
        if i <= j
            m(i+1,j+1) = ((-1)^(j-i)) * nchoosek(N,j) * nchoosek(j,i);
        end
    end
end
% Calculate C
T = sym(zeros(N+1,1));
for i = 1:length(T)
    T(i) = t^(i-1);
end
C = m * T;
x = 0;
y = 0;
for i = 1:N+1
    x = x + xcp(i)*C(i);
    y = y + ycp(i)*C(i);
end
% Convert syms to functions
getx = matlabFunction(x);
gety = matlabFunction(y);
% Polynomial regression
regt = linspace(0,1,8);
n = length(regt);
xreg = sym(zeros(n,1));
Yreg = sym(zeros(n,1));
for i=1:n
    xreg(i) = getx(L,regt(i));
    Yreg(i) = gety(Y2,Y3,Y4,Y5,Y6,regt(i));
end
Xreg = sym(zeros(n,n));
Xreg(:,1) = ones(n,1);
for i=1:(n-1)
    Xreg(:,i+1) = xreg.^i;
end
coef = inv(Xreg' * Xreg) * Xreg' * Yreg; %#ok<MINV>
s = 0;
for i=1:n
    s = s + coef(i)*(X^(i-1));
end
S = matlabFunction(s);
end