fzero function not working with symsum

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Iver Brekken
Iver Brekken 2022-2-7
编辑： Walter Roberson 2022-2-8
clear all
clc
close all
y = 0.5;
u = 0.25;
syms n t
fun = @(t) (-u + y-2/pi*symsum(1/n*sin(n*pi*(1-y))*exp(-(n*pi)^2*t),n,1,inf));
fzero(fun,0)
I want to find the root of the following (variable: t). I get the following error message:
Error using num2str (line 47)
Input to num2str must be numeric.
Error in fzero>errHandler (line 581)
sprintf('%g',y),num2str(fy)));
Error in fzero (line 346)
[b,fval,exitflag,output] = errHandler(a,fa,intervaliter,iter,fcount,trace,buildOutputStruct);
Error in a4_1 (line 9)
fzero(fun,0)
What can I do different?

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回答（1 个）

Walter Roberson
Walter Roberson 2022-2-7
Your symsum() is returning a symbolic value, so your fun() is returning a symbolic value -- but fzero requires the function to return single or double.
You should double() the results of the symsum.
  2 个评论
Iver Brekken
Iver Brekken 2022-2-7
clear all
clc
close all
y = 0.5;
u = 0.25;
syms n x
s = double(symsum(1/n*sin(n*pi*(1-y))*exp(-(n*pi)^2*x),n,1,inf));
fun = -u + y-2/pi*s;
fzero(fun,0)
Now i get this error message:
Error using symengine
Unable to convert expression containing symbolic variables into double array. Apply 'subs' function first to substitute values for variables.
Error in sym/double (line 702)
Xstr = mupadmex('symobj::double', S.s, 0);
Error in a4_1 (line 8)
s = double(symsum(1/n*sin(n*pi*(1-y))*exp(-(n*pi)^2*x),n,1,inf));
Walter Roberson
Walter Roberson 2022-2-8
编辑：Walter Roberson 2022-2-8
Ran in:
format long g
y = 0.5;
u = 0.25;
syms n x
s = symsum(1/n*sin(n*pi*(1-y))*exp(-(n*pi)^2*x),n,1,inf)
s = 
fun = -u + y-2/pi*s
fun = 
Fun = matlabFunction(fun, 'vars', x)
Fun = function_handle with value:
@(x)feval(@(n)symsum((exp(-n.^2.*x.*pi.^2).*sin((n.*pi)./2.0))./n,n,1.0,Inf),sym('n')).*(-6.366197723675814e-1)+1.0./4.0
FunW = @(x) double(Fun(x))
FunW = function_handle with value:
@(x)double(Fun(x))
location = fzero(FunW, [.09 .1])
location =
0.0946869595678489

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