How to form a function using 'for loop' without 'sym' command

Question

Bathala Teja 2021-9-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1447499-how-to-form-a-function-using-for-loop-without-sym-command

评论： Walter Roberson 2021-9-7

i tried like this

m = 150;
Aos = 40;
nAi = 0;
for i=1:2:m
    nAi = @(phi)nAi+cos(i*phi);
end
nA = vpa((nAi+Aos), 4)

Iam getting this error

Operator '+' is not supported for operands of type 'function_handle'.

Error in ll (line 8)

nA = vpa(nAi+Aos, 4)

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Jan 2021-9-6

You did not mention, what you try to achieve. All we see is the failing code. This is not enough information to guess, what you want to get instead.

Bathala Teja 2021-9-7

Its clearly there. i want to form nA interms of phi.

But i want to evalute without sym. Any idea.....

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Answer 1

Abolfazl Chaman Motlagh 2021-9-6

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https://ww2.mathworks.cn/matlabcentral/answers/1447499-how-to-form-a-function-using-for-loop-without-sym-command#answer_781699

Assuming you want nA be function of phi, you can use symsum for summuation :

m = 150;
Aos = 40;
syms phi k
nAi =@(phi) symsum(cos(2*k*phi),k,1,m/2);
nA =@(phi)  vpa((nAi(phi)+Aos), 4);
% example
nA(pi)
ans = 115.0

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Walter Roberson 2021-9-6

syms is an abbreviation for sym() so this does not satisfy the requirement to not use sym

Abolfazl Chaman Motlagh 2021-9-6

Oh! sorry, i just read the content not title of question.

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Answer 2

Walter Roberson 2021-9-6

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https://ww2.mathworks.cn/matlabcentral/answers/1447499-how-to-form-a-function-using-for-loop-without-sym-command#answer_781704

m = 150;
Aos = 40;
nAi = @(phi) zeros(size(phi));
for i=1:2:m
    nAi = @(phi)nAi(phi)+cos(i*phi);
end
nA = @(phi) nAi(phi)+Aos
nA = function_handle with value:
    @(phi)nAi(phi)+Aos

You asked to avoid sym, so it seems likely to me you want to avoid using vpa() as well. But if using a final vpa is okay, then

vpa(nA, 4)

ans =

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Bathala Teja 2021-9-7

编辑：Bathala Teja 2021-9-7

How to show result like this(ans which you shared) without vpa??

And you got result in the form of phi(means symbol), how to get symbol in place of phi??

Walter Roberson 2021-9-7

With vpa(), the symbol for phi appears if you are using LiveScript, but not for traditional .m files.

To get the result without using vpa:

m = 150;
Aos = 40;
nA = str2func("@(phi) " + strjoin(compose("cos(%d*theta)", 1:2:m), " + ") + " + " + string(Aos))
nA = function_handle with value:
    @(phi)cos(1*theta)+cos(3*theta)+cos(5*theta)+cos(7*theta)+cos(9*theta)+cos(11*theta)+cos(13*theta)+cos(15*theta)+cos(17*theta)+cos(19*theta)+cos(21*theta)+cos(23*theta)+cos(25*theta)+cos(27*theta)+cos(29*theta)+cos(31*theta)+cos(33*theta)+cos(35*theta)+cos(37*theta)+cos(39*theta)+cos(41*theta)+cos(43*theta)+cos(45*theta)+cos(47*theta)+cos(49*theta)+cos(51*theta)+cos(53*theta)+cos(55*theta)+cos(57*theta)+cos(59*theta)+cos(61*theta)+cos(63*theta)+cos(65*theta)+cos(67*theta)+cos(69*theta)+cos(71*theta)+cos(73*theta)+cos(75*theta)+cos(77*theta)+cos(79*theta)+cos(81*theta)+cos(83*theta)+cos(85*theta)+cos(87*theta)+cos(89*theta)+cos(91*theta)+cos(93*theta)+cos(95*theta)+cos(97*theta)+cos(99*theta)+cos(101*theta)+cos(103*theta)+cos(105*theta)+cos(107*theta)+cos(109*theta)+cos(111*theta)+cos(113*theta)+cos(115*theta)+cos(117*theta)+cos(119*theta)+cos(121*theta)+cos(123*theta)+cos(125*theta)+cos(127*theta)+cos(129*theta)+cos(131*theta)+cos(133*theta)+cos(135*theta)+cos(137*theta)+cos(139*theta)+cos(141*theta)+cos(143*theta)+cos(145*theta)+cos(147*theta)+cos(149*theta)+40