MaplePrimes - answers and comments on Question, Why won't Maple use my assumptions in a double integral?

assume or assuming?

Carl Love — Fri, 01 Feb 2013 05:35:15 Z

How are you making the assumptions, with assume or assuming? And does the variable upon which the assumptions are made come from a function call, but other than as a parameter to that function? If you're using assuming, then that's the problem. For example, the following works:

restart;
assume(k<0);
f:= x-> exp(k*x): # k in function, but is not a parameter
int(f(x), x= 0..infinity);

-1/k

But in the following, the assumption is ignored:

restart;
f:= x-> exp(k*x): # k in function, but is not a parameter
int(f(x), x= 0..infinity) assuming k < 0;

limit((exp(k*x)-1)/k, x = infinity)

The assumptions made with assuming are only applied to variables which appear in the expression before it is evaluated.

Need "additionally"

Carl Love — Fri, 01 Feb 2013 06:02:52 Z

Your assume(Rmin < Rmax) needs to be replaced with additionally(Rmin < Rmax). Multiple assume commands on the same variable are not cumulative. I tested this on your code snippet, and with the additionally it integrates fine. So, no need to upload tomorrow.

But, In the future, please cut-and-paste at least a snippet of code into your original posts, or upload a worksheet. Even a poorly written question with a code example is easier to answer than a well-written question with no code example.

I'm using "assume"

spradlig — Fri, 01 Feb 2013 05:49:33 Z

Carl:

I'm using "assume" Here's the code and the output

> restart:

> assume(Rmin>0):assume(Rmax>0):assume(Rmin<Rmax):

> DiceZero:=(Rmin,Rmax)->2/(Rmax-Rmin)^2*int(int(r0^3/(r0^3+r1^3),r0=Rmin..r1),r1=Rmin..Rmax);

DiceZero := proc (Rmin, Rmax) options operator, arrow; 2*(int(int(r0^3/(r0^3+r1^3), r0 = Rmin .. r1), r1 = Rmin .. Rmax))/(Rmax-Rmin)^2 end proc

> DiceZero(Rmin,Rmax);#doesn't work despite adequate assumptions

undefined/(Rmax-Rmin)^2

I can upload the real mw-file tomorrow

Greg

Thanks

spradlig — Fri, 01 Feb 2013 06:41:12 Z

Thanks, I'll try that. I thought I cut-and-pasted the file into a Word document and uploaded it, but maybe I goofed. I'll make sure to do that the first time I post next time.

Works like a charm. Thanks for your prompt and perfect solution.

No Word docs, please

Carl Love — Fri, 01 Feb 2013 07:01:28 Z

@spradlig

Plain text is easiest to work with. Use one of the three clipboard icons on the toolbar in MaplePrimes to cut-and-paste directly into your post. Maple understands plaintext, but not Word AFAIK. Or upload a worksheet. Why take the extra step of going through Word?

Thanks, I won't do it again.

spradlig — Fri, 01 Feb 2013 17:35:38 Z

@Carl

Thanks, I won't upload a Word doc again.