Sdk: [ask] how to use log(x) with base number

[cacing69]

i have a new on dart programming, so i need to use this function on my program to find log() with base number

so for example on php, i used like this

PHP log() function
how can i solve this on dart ?

[lrhn]

Dart does not currently have an arbitrary base logarithm function, only base e (log). This is most likely inherited from JavaScript, which also only provides these two.

In general, the logarithm at one base, b₁, can be found using the logarithm at any other base, b₂ as log_b1(x) = log_b2(x) / log_b2(b₁).

So, to find the base-10 logarithm of 5 using only the natural logarithm (base e), you can write log(5)/log(10). The constant log(10) is available as ln10, so it can also be written log(5)/ln10.

If it happens often, you can define your own functions:

double logBase(num x, num base) => log(x) / log(base);
double log10(num x) => log(x) / ln10;

[cacing69]

Thanks you very much for explanation @lrhn

[cacing69]

@lrhn So if i want to chane base to 1000 just make

double log1000 =  log(9000) / log(1000)

[lrhn]

That should compute log_1000(9000). You can see that the result changes by 1 when you change the 9000 value by a factor of 1000:

print(log(9000) / log(1000)); // 1.3180808364797751
print(log(9000000) / log(1000)); // 2.318080836479775
print(log(9) / log(1000)); // 0.318080836479775
print(pow(1000, log(9000) / log(1000)); // 9000.000000000011

That is the correct behavior for a base-1000 logarithm (with a little rounding).

[cacing69]

Ahh thank you , now i can understand