*** Write a function called triangle_wave that computes the sum (−1) sin(2 +1) (2 +1) for each of 1001 values of t uniformly spaced from 0 to 4π inclusive. The input argument is a scalar non-negative integer n, and the output argument is a row v

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Wasi von Deutschland 2017-5-20

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评论： Vikrant dhall 2018-4-29

采纳的回答： Jan

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this is my code and I need your help I couldn't figure out where I'm making mistake.

function theSum = triangle_wave(n)
t = linspace(0, 4*pi, 1001);
for tIndex = 1 : length(t)
  this_t = t(tIndex);
  k = 1 : n;
  numerator = ((-1)^k).*sin(this_t * (2*k+1));
  denominator = (2 * k + 1)^2;
  theSum(tIndex) = sum(numerator ./ denominator);
end

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Wasi von Deutschland 2017-5-21

@ stephen I'm really sorry. Next I will keep this in mind.

Jan 2017-5-21

@Waseem Iqbal: It is okay. This happens frequently and we all remind newcomers to improve the format. Now let's come back to the question for clarification:

You forgot to mention, why you assume that there is a mistake. Please explain this.

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Jan 2017-5-21

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编辑：Jan 2017-5-21

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denominator = (2 * k + 1) .^ 2;

Use the elemtnwise .^ instead of the matrix operation ^ . The same for "(-1)^k" .

The corresponding error message is clear:

 Error using  ^ 
 Inputs must be a scalar and a square matrix.
 To compute elementwise POWER, use POWER (.^) instead.

[EDITED] The formula contains: "Sum from k=0 to n", you code contains:

k = 1:n;

Replace this by k = 0:n. It will be more efficient to move the definition before the loop and pre-allocate the output:

function S = triangle_wave(n)                                      
t = linspace(0, 4*pi, 1001);
S = zeros(size(t));   % Pre-allocation
k = 0:n;              % Not 1:n
for tIndex = 1 : length(t) 
  numerator   = ((-1) .^ k) .* sin(t(tIndex) .* (2 * k + 1));
  denominator = (2 .* k + 1) .^ 2;
  S(tIndex)   = sum(numerator ./ denominator);
end

@Waseem: Look at the formula: Look at the limits of the sum, it goes from k = 0 to n. Do you see it under and above the Sigma? With the zeros() command I've pre-allocated the output. Search in this forum for "pre-allocation".

rishabh gupta 2018-2-10

can you please tell how is the value of k changing when it is placed outside the loop??

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Walter Roberson 2017-5-21

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(-1)^k needs to be (-1).^k

(2 * k + 1)^2 needs to be (2 * k + 1).^2

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Vikrant dhall 2018-4-29

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function v = triangle_wave(n) t = linspace(0,4 * pi, 1001); v = zeros(size(t)); p = 1; for tt = 0:length(t) suma = 0; for k = 0:n suma = suma + (((-1 .^ k) .* sin((2.*k+1).*tt)) / ((2.* k+1).^2)); %suma end %suma v(1,p) = suma; p = p + 1; end end

What is the error in this can anyone please help

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Vikrant dhall 2018-4-29

在 MATLAB Online 中打开

function v = triangle_wave(n)

if true
  % code
end
t = linspace(0,4 * pi, 1001);
v = zeros(size(t));
p = 1;
for tt = 0:length(t)
  suma = 0;
  for k = 0:n
      x = ((-1 .^ k) .* sin((2.*k+1).*tt)) / ((2.* k+1).^2);
      suma = suma + x;
      %suma
  end
  %suma
  v(1,p) = suma;
  p = p + 1;
end
end