Is this correct?

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Allison Sims
Allison Sims 2022-7-18
评论： Chunru 2022-7-18
Ran in:
Use loops to compute and plot (not animated)the following piecewise function for -15<=x<=15 .
F(x)={5x, x<0
{x^2, 0<=x<2
{ 2lnx, x>=2
My code:
x=-15:15;
if x<0;
5*x;
elseif x>=0 & x<2
y=x^2;
else x>=2;
y=2*log(x);
end
plot(x,y)
Warning: Imaginary parts of complex X and/or Y arguments ignored.
  4 个评论
显示 2更早的评论
M.B
M.B 2022-7-18
Check your variable names and indexation.
Chunru
Chunru 2022-7-18
Although the code is not doing what it intends to, the code can be run and MATLAB only gives a warning message (orange color).

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采纳的回答

Chunru
Chunru 2022-7-18
Ran in:
x=-15:15;
y = zeros(size(x));
% This is more MATLAB way
idx = x<0;
y(idx) = 5 * x(idx);
idx = x>=0 & x<2;
y(idx) =x(idx).^2;
idx = x>=2;
y(idx) = 2*log(x(idx));
plot(x,y)
% This is more conventional way (some othter programming language)
x=-15:15;
y = zeros(size(x));
for i=1:length(x)
if x(i)<0
y(i) = 5 * x(i);
elseif x(i)>=0 & x(i)<2
y(i) =x(i).^2;
elseif x(i)>=2;
y(i) = 2*log(x(i));
end
end
figure
plot(x,y)

更多回答（1 个）

M.B
M.B 2022-7-18
Ran in:
x = -15:1:15;% init x
y = nan*x;% init y to be of same size as x
for index = -15:15;
if index<0;
y(index+16) = 5*index;
elseif index>=0 & index<2
y(index+16) = index^2;
else index>=2;
y(index+16) = 2*log(index);
end
end
plot(x,y)
  2 个评论
Allison Sims
Allison Sims 2022-7-18
what does the y(index+16) mean?
Chunru
Chunru 2022-7-18
The "index" is the loop variable the code uses and it need to be added with 16 in order to become array index (which is 1,2,...31). It's working code, but it may be further improved.

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