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How can I simplify numerical calculations in symbolic math toolbox?

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Antonio
Antonio 2015-10-16
评论： Walter Roberson 2015-10-16
Hi there,
When I write this:
fR == simplify((Alpha/uR)*((y/uR)^(Alpha-1))*exp(-(uS/y)^k))
I get something like this:
fR =
(12153*exp(-(10/y)^(601/100))*(y/20)^(11153/1000))/20000
Could you tell me please how to simplify the numerical calculations?! I mean I want the term "(11153/1000))/20000" be printed as "0.000557".
Thanks

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Star Strider
Star Strider 2015-10-16
Use the vpa function. (If you want to solve an equation and avoid fractions, use the vpasolve function.)
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Star Strider
Star Strider 2015-10-16
Actually, that’s essentially what you want. It’s just expressing the decimal fractions literally instead of as decimals. However, I’m not quite certain why it’s rendering, for instance, (11153/1000) as a fraction and not as 11.153. Maybe close enough is good enough for vpa. (I get the same result as you do.)
Walter Roberson
Walter Roberson 2015-10-16
Exponents are not converted to floating point because a floating point exponent means something different than a rational exponent. With rational exponents you need to worry about multiple roots and principle roots, but with floating point exponent the operation x^(a/b) is defined strictly in terms of exp(a/b * log(x)) which is a single value that is complex in cases where algebraic x^(a/b) might be real-valued.

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