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

Question

Tomas 2023-5-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1956474-error-invalid-expression-when-calling-a-function-or-indexing-a-variable-use-parentheses-otherwis

评论： Image Analyst 2023-5-2

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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Answer 1

Walter Roberson 2023-5-2

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https://ww2.mathworks.cn/matlabcentral/answers/1956474-error-invalid-expression-when-calling-a-function-or-indexing-a-variable-use-parentheses-otherwis#answer_1227384

在 MATLAB Online 中打开

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])

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Tomas 2023-5-2

Thank you! That is correct. I'm still getting used to the program.

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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