a bug of "plotode"?

[kilasuelika]

I have been always getting "invalid dimension" errors when I tried to plotode(x*sin(y),[x y],[-2 2]) just as the user guide told.
   
   
It's so annoying. Is there anyone who has been succeeded in plotode?

[parisse]

Try with a precise interval in x

Code:

plotode(x*sin(y),[x=-10..10,y],[-2,2])

otherwise autoscaling fails. Indeed the general solution is

Code:

desolve(y'=x*sin(y))

Code:

2*atan(exp(x^2/2)/c_0)+2*n_1*pi

therefore the limit (2k+1)*pi is reached very fast (because of the exponential), and the y-scaling algorithm fails.

[kilasuelika]

(03-18-2016 04:03 PM)parisse Wrote:  Try with a precise interval in x

Code:

plotode(x*sin(y),[x=-10..10,y],[-2,2])

otherwise autoscaling fails. Indeed the general solution is

Code:

desolve(y'=x*sin(y))

Code:

2*atan(exp(x^2/2)/c_0)+2*n_1*pi

therefore the limit (2k+1)*pi is reached very fast (because of the exponential), and the y-scaling algorithm fails.

In fact, when I tried to plotode(x*sin(y),[x=-10..10,y],[-2,2]), it shows "Bad argument value". Now I am confused what can we do use plotode.
   

At the same time, desolve(y'=x*sin(y)) or desolve(y'=x*sin(y), x, y) doesn't work.
   

[parisse]

Make sure that x and y are not assigned (purge(x,y))

[kilasuelika]

(03-18-2016 07:06 PM)parisse Wrote:  Make sure that x and y are not assigned (purge(x,y))

Yes, it is! I forgot that I had assigned a value to x.
Thank you so much

[leprechaun]

Recently I thought about trouble like the above with assigned variables or somehow similar capital X in combination with home and cas commands.

Would it be an option to print the expression with replaced variables if an error occured? That would not make you save if your assigment yields a formally correct expression and just returns an 'incorrect' result. But if the calculator reports an error it could be really helpful to see, what expression was actually evaluated. ?