Error: Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters

2023 5 2
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更新时间：2023 5 2
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This is the code that I have so far. Up until t = linspace(0,2*pi); I do not get any errors. I'm unsure if i have to start a new thread for the second part of this question, but I'm also wondering how would one be able to write a generic code for this type of task.
x = -1 + 2.*rand (1,n)
y = -1 + 2.*rand (1,n)
appr = (sum(x.*sin(1./x)<=1)/n)*4
plot(x(x.*sin(1./x)<=1),y(x.*sin(1./x)<=1),".", ... "Color",[0.3 0.7 0.5], "MarkerSize",10)
hold on
plot(x(x.*sin(1./x0,y(x.*sin(1./x),".", ... "Color", [0.7 0.5 0.3], "MarkerSize",10)
t = linspace(0,2*pi);
plot(cos(t),sin(t),’LineWidth’,3,’Color’,[0.1 0.3 0.5])

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回答（1 个）

Walter Roberson
Walter Roberson 2023-5-2
Ran in:

0 个投票

Ran in:
I had to guess about what you are trying to do.
n = 50;
x = -1 + 2.*rand (1,n)
x = 1×50
-0.5991 -0.5210 -0.7474 -0.9179 0.2134 0.7822 0.5500 -0.3415 0.1121 -0.2442 0.9066 0.9617 -0.0918 -0.8584 -0.8393 -0.8383 -0.3599 -0.0121 -0.0055 -0.0096 0.1896 0.8881 -0.6809 -0.4161 -0.1603 -0.6235 -0.2973 0.5422 0.5792 0.9235
y = -1 + 2.*rand (1,n)
y = 1×50
-0.1821 0.4905 0.6683 -0.8477 -0.1780 -0.9238 -0.8321 0.4223 -0.7923 -0.7137 0.5017 0.9251 -0.5448 0.2657 0.3568 -0.6313 -0.0869 -0.1506 -0.2911 -0.3678 -0.7103 0.6023 0.3364 -0.1782 -0.6253 -0.1144 0.0615 0.5388 0.8450 -0.3836
appr = (sum(x.*sin(1./x)<=1)/n)*4
appr = 4
plot(x(x.*sin(1./x)<=1),y(x.*sin(1./x)<=1),".", ...
"Color",[0.3 0.7 0.5], "MarkerSize",10)
hold on
plot(x(x.*sin(1./x)>1),y(x.*sin(1./x)>1),".", ...
"Color", [0.7 0.5 0.3], "MarkerSize",10)
t = linspace(0,2*pi);
plot(cos(t),sin(t),"LineWidth",3,"Color",[0.1 0.3 0.5])

5 个评论
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Tomas
Tomas 2023-5-2
That is pretty much what I am trying to do. It doesn't look like there's any difference between our t line. Did you do anything differently then what I had previously written?
Walter Roberson
Walter Roberson 2023-5-2
Your version had
plot(x(x.*sin(1./x)<=1),y(x.*sin(1./x)<=1),".", ... "Color",[0.3 0.7 0.5], "MarkerSize",10)
Everything after the ... on a line is a comment.
Your version had
plot(x(x.*sin(1./x0,y(x.*sin(1./x),".", ... "Color", [0.7 0.5 0.3], "MarkerSize",10)
which has x0 instead of x) and is missing the ) for y(x.*sin(1./x) and is missing the >1 that I presumed are desired to indicate points that do not match with the criteria.
Walter Roberson
Walter Roberson 2023-5-2
By the way, consider
mask = x.*sin(1./x)<=1;
plot(x(mask), y(mask), stuff)
plot(x(~mask), y(~mask), stuff)
Much simpler and much less error prone.
Tomas
Tomas 2023-5-2
Thank you! That is correct. I'm still getting used to the program.
Image Analyst
Image Analyst 2023-5-2
If this Answer solves your original question, then could you please click the "Accept this answer" link to award the answerer with "reputation points" for their efforts in helping you? They'd appreciate it. Thanks in advance. 🙂 Note: you can only accept one answer (so pick the best one) but you can click the "Vote" icon for as many Answers as you want. Voting for an answer will also award reputation points.

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