CalcLog

CalcLog[ x, b ] calculates the logarithm of x with base b, if the result is exact.

Usages

`CalcLog[ x, b ]`

CalcLog[ x, b ] calculates ^blog(x): the exponent to which b must be raised to get x. Note that the number comes first and the base second. The result is only calculated if it is an integer; otherwise CalcLog is left unevaluated (use Numerical for a decimal approximation).

Example	in	out
`10² = 100`.	`CalcLog[ 100, 10 ]`	`2`
`2³ = 8`.	`CalcLog[ 8, 2 ]`	`3`
A fraction.	`CalcLog[ 1/8, 2 ]`	`-3`
A decimal number.	`CalcLog[ 0.001, 10 ]`	`-3`
A power of the base.	`CalcLog[ 2^5, 2 ]`	`5`
The result is not an integer, so it is not calculated.	`CalcLog[ 10, 2 ]`	`CalcLog[10, 2]`
A decimal approximation.	`Numerical[ CalcLog[10, 2], 3 ]`	`3.322`

Details

Undefined logarithms: a number that is 0 or negative, or a base that is 1, 0 or negative, gives NaN: CalcLog[ 0, 2 ] and CalcLog[ 8, 1 ] give NaN.
The base is required: CalcLog[ 100 ] is left unevaluated.
Lists are not supported: CalcLog[ {8, 16}, 2 ] is left unevaluated. Use Map.
Natural logarithm: CalcLog[ EulerE, EulerE ] is left unevaluated. Use Ln with Simplify or Numerical.

See also: CalcPower, Numerical, Math functions