
From:  Brett Green 
Subject:  Re: Plotting curves defined by implicit functions 
Date:  Thu, 19 Sep 2019 18:43:57 0400 
> Il giorno 17 set 2019, alle ore 07:02, address@hidden ha scritto:
>
>
>
>> Il giorno 16 set 2019, alle ore 16:55, Brett Green <address@hidden> ha scritto:
>>
>> Thank you! I've used contours for this before, and was wondering if there was an alternative method streamlined for level curves, but that's probably just a pipe dream.
>>
>> On that subject, though, I have an issue with contour. Either I'm doing something mathematically inane or I'm misunderstanding how to call the function. I rune the code:
>>
>> F = @(x,y) x.^2+y.^24;
>> x=linspace(5,5,100);
>> y=x;
>> for k=1:100
>> for j=1:100
>> Fmat(k,j) = F(x(k),y(j));
>> end
>> end
>> contour(x,y,Fmat,0)
>>
>> and get
>>
>> warning: division by zero
>> warning: called from
>> __contour__ at line 167 column 11
>> contour at line 74 column 18
>>
>> I thought I asked for a contour where Fmat=0, which should be a circle of radius 2. What am I missing here?
>>
>>  Brett Green
>
>
>
>>> F = @(x,y) x.^2+y.^24;
>>> [x, y] = meshgrid (linspace (5,5,100));
>>> contour (x, y, F(x, y))
>
>
> have a look at meshgrid in the manual.
> c.
BTW, I think the best way to plot the curve you want in the example is
F = @(x, y) x.^2 + y.^2;
contour (x, y, F(x,y), [4 4]);
The form for the last input is not documented clearly in the manual, I
just posted a documentation bug about this here :
https://savannah.gnu.org/bugs/?56907
c.
[Prev in Thread]  Current Thread  [Next in Thread] 