Android Question How do I use exponential math?

stevel05

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• Aug 4, 2014

• #2

Use the Power Function:

B4X:

Power (Base As Double, Exponent As Double) As Double
'Returns the Base value raised to the Exponent power.

 

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Levisvv

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• Aug 4, 2014

• #3

The following is giving me an error:

B4X:

Dim FLrate As Double
Dim DRVqty As Int
DRVqty=4
Dim Frate As Double
Frate=.0035

FLrate= 1 - ((1-Frate) ^ DRVqty)

 

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stevel05

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• Aug 4, 2014

• #4

The ^ is not a valid operator, you need to use the power function.

Try Using:

FLrate= 1 - Power(1-Frate, DRVqty)

 

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Levisvv

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• Aug 4, 2014

• #5

that worked stevel05 thx.

 

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L

Levit

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• Aug 4, 2014

• #6

try this :
FLrate = 1 - (Power(1-Frate, DRVqty))

 

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JohnD

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• Aug 4, 2014

• #7

Beware when using 3 to the power of 3 with the Power() function.

B4X:

Dim p3 = 3 As Double
Log(Power(p3,p3))

Will produce: 26.99999999999999

 

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sirjo66

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• Aug 4, 2014

• #8

The problem is not number "3", the problem is that you are using double numbers
Try:

B4X:

Dim p3 = 3 As Int

 

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JohnD

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• Aug 4, 2014

• #9

sirjo66 said:

The problem is not number "3", the problem is that you are using double numbers
Try:

B4X:

Dim p3 = 3 As Int

Click to expand...

Nope. Does the same thing with number 3 as an Int.

 

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sirjo66

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• Aug 4, 2014

• #10

Yes, you are right, but it's the same.
The problem is that the parameters of Power function is double type, so the system convert p3 from Int to Double type, and we know that double type has a precision problem because it isn't bit-bit (like an Int) but is representive by mantissa and exponent, so you can have a precision problem (like, for example numer 3).

Sergio

 

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JohnD

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• Aug 4, 2014

• #11

I saw this originally in the unit testing for my Pre-Algebra Tester app. Since the largest exponent in that program is 4, I didn't use Power(). I took the more pedestrian but safer route of multiplying.

 

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