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JonathanStevens1-Visitor
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May 19, 2011
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Basic Triple Integral Question, How to get Exact results?

  • May 19, 2011
  • 1 reply
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Sorry for the basic question. I am trying to do some simple spherical coordinate integration but my results are not coming out exact, or not coming out at all. I am a MathCAD newbie and have been trying to figure out what the problem is to no avail. Using MathCAD 15.

I assume it is possible to get exact results and not just a very precise decimal number? And also to use variables in the integrand that are defined in the definite integral's limits and will be given values.

Best answer by StuartBruff

Jonathan Stiefel wrote:

Sorry for the basic question. I am trying to do some simple spherical coordinate integration but my results are not coming out exact, or not coming out at all. I am a MathCAD newbie and have been trying to figure out what the problem is to no avail. Using MathCAD 15.

I assume it is possible to get exact results and not just a very precise decimal number? And also to use variables in the integrand that are defined in the definite integral's limits and will be given values.

Mathcad (in common with other symbolic applications) doesn't treat sinx as sine of x; it's a variable name. You either have to write sin(x) or, in Mathcad's case, use the prefix operator, which allows sin x.

Additionally, symbolic processors tend to treat floating point expressions as instructions to return a floating point result - the fp numbers are stored and handled differently (although 1.5 is 3/2, not all fp numbers can be reduced to rational form and it attempts to treat expressions consistently).

Stuart

1 reply

S
StuartBruff23-Emerald VAnswer
23-Emerald V
May 19, 2011

Jonathan Stiefel wrote:

Sorry for the basic question. I am trying to do some simple spherical coordinate integration but my results are not coming out exact, or not coming out at all. I am a MathCAD newbie and have been trying to figure out what the problem is to no avail. Using MathCAD 15.

I assume it is possible to get exact results and not just a very precise decimal number? And also to use variables in the integrand that are defined in the definite integral's limits and will be given values.

Mathcad (in common with other symbolic applications) doesn't treat sinx as sine of x; it's a variable name. You either have to write sin(x) or, in Mathcad's case, use the prefix operator, which allows sin x.

Additionally, symbolic processors tend to treat floating point expressions as instructions to return a floating point result - the fp numbers are stored and handled differently (although 1.5 is 3/2, not all fp numbers can be reduced to rational form and it attempts to treat expressions consistently).

Stuart

S
StuartBruff23-Emerald V
23-Emerald V
May 19, 2011

Stuart Bruff wrote: ..

Jonathan Stiefel wrote:

...

Forgot to add ... in your last example, if you want a single number result, rather than an expression involving pi (or some other 'number'), then use the symbolic 'float' command.

Stuart

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