about the problem 'Unable to generate code for piecewise for use in anonymous functions', thanks

hello, every

my code

syms l xita miu h n t1 gfi
fai = pi-2*atan(l*sind(xita)/(h+l*cosd(xita)));
ti=t1*exp(-(gfi+1)*miu*(fai));
ui1i=[(-1)^(gfi-1)*(h+2*l*cosd(xita));-1*l*sind(xita)];
dfui1i=diff(ui1i,xita);
qti=-1*ti*ui1i'/sqrt(ui1i(1)^2+ui1i(2)^2)*dfui1i;
qt=symsum(qti,gfi,1,n);
F=matlabFunction(qt);

does not work.

I got this error:

Error using symengine
Unable to generate code for piecewise for use in anonymous functions.
Error in sym/matlabFunction>mup2mat (line 404)
res = mupadmex('symobj::generateMATLAB',r.s,ano,spa,0);
Error in sym/matlabFunction>mup2matcell (line 374)
    r = mup2mat(c{1},true,sparseMat);
Error in sym/matlabFunction (line 188)
    body = mup2matcell(funs, opts.Sparse);

Could you please help me with this issue?

thank you!

Answer 1

[Walter Roberson]

The message is correct: piecewise() cannot be built into an anonymous funciton. However it can be coded into a function if you tell matlabFunction to write to a file.

syms l xita miu h n t1 gfi
assume(n, 'integer')
assumeAlso(n>=1)
Pi = sym(pi);

fai = Pi-2*atan(l*sind(xita)/(h+l*cosd(xita)));
ti = t1*exp(-(gfi+1)*miu*(fai));
ui1i = [(-1)^(gfi-1)*(h+2*l*cosd(xita)); -1*l*sind(xita)];
dfui1i = diff(ui1i,xita);
qti = simplify(-1*ti*ui1i'/sqrt(ui1i(1)^2+ui1i(2)^2)*dfui1i)

qti = 

qt = symsum(qti,gfi,1,n);

qt

qt = 

tn = [tempname, '.m'];
F = matlabFunction(qt, 'file', tn, 'optimize', true)

F = function_handle with value:
    @tpd90ebd4f_b5a5_4140_8679_8b7468e23d90

type(tn)

function qt = tpd90ebd4f_b5a5_4140_8679_8b7468e23d90(h,l,miu,n,t1,xita)
%TPD90EBD4F_B5A5_4140_8679_8B7468E23D90
%    QT = TPD90EBD4F_B5A5_4140_8679_8B7468E23D90(H,L,MIU,N,T1,XITA)

%    This function was generated by the Symbolic Math Toolbox version 8.7.
%    09-Sep-2021 10:27:32

t3 = conj(h);
t4 = abs(l);
t5 = conj(xita);
t6 = miu.*pi;
t7 = l.^2;
t8 = n+1.0;
t11 = 1.0./l;
t15 = (xita.*pi)./1.8e+2;
t9 = t4.^2;
t10 = exp(t6);
t12 = -t6;
t14 = t6.*t8;
t16 = (t5.*pi)./1.8e+2;
t17 = cos(t15);
t18 = sin(t15);
t13 = 1.0./t10;
t19 = cos(t16);
t20 = sin(t16);
t21 = l.*t17;
t22 = t18.^2;
t25 = t3.*t18.*2.0;
t23 = t21.*2.0;
t24 = h+t21;
t27 = t7.*t22;
t32 = t9.*t11.*t17.*t20;
t33 = t9.*t11.*t18.*t19.*4.0;
t26 = h+t23;
t28 = 1.0./t24;
t34 = -t32;
t29 = t26.^2;
t30 = l.*t18.*t28;
t40 = t25+t33+t34;
t31 = atan(t30);
t36 = t27+t29;
t35 = miu.*t31.*2.0;
t38 = 1.0./sqrt(t36);
t37 = exp(t35);
t39 = t13.*t37;
if (t39 == 1.0)
    qt = (l.*n.*t1.*t38.*t40.*pi)./1.8e+2;
elseif (t39 ~= 1.0)
    qt = (l.*t1.*t39.*pi.*exp(t8.*t12).*1.0./sqrt(t27+(h+t23).^2).*(t10.*exp(t8.*t35)-t37.*exp(t14)).*(t25+t33+t34).*(-1.0./1.8e+2))./(t10-t37);
else
    qt = NaN;
end

You can use a different file name for tn -- the one tempname() I use here generates a random file name in a temporary directory.

Be careful: when you code generate for piecewise() into a file, then the result is not a vectorized function !

[binbin cao]

IT WORKS!

Thank you so much.

Best regards

[binbin cao]

I have one more question：

the formula that you paste is very pretty，how can i output my formula like that

[Walter Roberson]

LiveScript will display like that.

[binbin cao]

ok，thank you

[Walter Roberson]

By the way: the special condition that leads to the branch, is arguably true when

xita = 180 - (180*acos(h/l))/pi 

But that has to be taken in the limit, and one side of the limit has a different value.

Under that condition, in the limit, the denominator of namely becomes 0, but the numerator is positive so that becomes infinity, and arctan(infinity) is pi/2 which is the condition that leads to . So division by 0 but in the context of an arctan that knows how to deal with infinity, so no actual singularity in context. Which is why you can get a solution under that condition without an exception.

If there is some constraint such that xita cannot pass through that value, then you could

children(qt,2)

and use that instead of qt: it will not need piecewise() in that case. But if it can pass through that value then you need the full expression.