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

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]) 

Answer 1

[Walter Roberson]

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]) 

[Tomas]

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]

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]

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]

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

[Image Analyst]

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