build functions with str2func command in matlab - matlab

Question

I want to build a series of different function with matlab and integrate and differentiate the results. but the mathwork says the output of the str2func can't access the variable or could bot be used by other function.
Is any one help me with this problem?
I want to create these function:
f1= #(x,l) x.*(l-x);
f2= #(x,l) x.^2.*(l-x).^2.*(l/2-x).^2;
f3= #(x,l) x.^3.*(l-x).^3;
f4= #(x,l) x.^4.*(l-x).^6.*(l/2-x).^4;
f5= #(x,l) x.^5.*(l-x).^5;
f6= #(x,l) x.^6.*(l-x).^6.*(l/2-x).^6;
f7= #(x,l) x.^7.*(l-x).^7;
f8= #(x,l) x.^8.*(l-x).^8.*(l/2-x).^8;
f9= #(x,l) x.^9.*(l-x).^9;
f10= #(x,l) x.^10.*(l-x).^10.*(l/2-x).^10;
I write this function:
syms x l
f=cell(10,1);
fun=cell(10,1);
for i=1:10
if mod(i,2) ~= 0
f{i}=['x','.^',num2str(i),'.*','(l-x)','.^',num2str(i)];
else
f{i}=['x','.^',num2str(i),'.*','(l-x)','.^',num2str(i),'.*','(l/2-x)','.^',num2str(i)];
end
end
for i=1:10
for j=1:10
if mod(i,2) ~= 0 & mod(j,2) ~= 0
Fs = ['(x)','x','.^',num2str(i),'.*','(l-x)','.^',num2str(i),'*','x','.^',num2str(j),'.*','(l-x)','.^',num2str(j)];
FS = str2func (Fs)
fjnew = str2func(['(x)','x','.^',num2str(j),'.*','(l-x)','.^',num2str(j)])
fj_diff = diff(fjnew,x)
when I run that the error is :
Undefined function '(x)x.^1.*(l-x).^1' for input arguments of type 'sym'.
Error in sym>funchandle2ref (line 1172)
S = x(S{:});
Error in sym>tomupad (line 989)
x = funchandle2ref(x);
Error in sym (line 142)
S.s = tomupad(x,'');
Error in sym/privResolveArgs (line 810)
argout{k} = sym(arg);
Error in sym/diff (line 21)
args = privResolveArgs(S,varargin{:});
Your Sincerely
Saeed Nasiri

Answer 1

I found all your problems.
The character "l" is not the character "1". One of them is L and the other is a number. You just wrote "l" \ell\ instead of "1" \one\ in (l-x). EDIT I just realised you actually want l not 1.
Function handles are not (x)x.^2 (random example), they are #(x)x.^2! You forgot to add the "#" in all the calls, thus =['(x)' should be =['#(x)'
3.Your functions are actually (as yourself described in the post), variable respect x and l. Thus, you need the function handle to say that. Change =['#(x)' for =['#(x,l)'.
Iam not sure if you are aware of this, but you dont use practically any of the parts of your code. Your code can be reduced to 4 lines and it will do exactly the same. Fs,FS adn f are never use.:
The result of your code is the same as:
for i=1:10
for j=1:10
if mod(i,2) ~= 0 & mod(j,2) ~= 0
fjnew = str2func(['#(x,l)','x','.^',num2str(j),'.*','(l-x)','.^',num2str(j)])
fj_diff = diff(fjnew,x)
end
end
end
So unless you are doing more stuff with it later, there is no need to compute stuff unnecessarily.