#### Archived

This topic is now archived and is closed to further replies.

# logarithm

This topic is 6167 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

is anyone aware of an algorithm to compute logarithm other than the Tayler series method? thanx for any responses.

##### Share on other sites
Here's a little recursive algorithm due to John Napier (16th century).

//Globals defined outside of function for claritystatic double aMean = -1.0;  //arithmetic meanstatic double gMean = -1.0;  //geometric meanstatic double precision = 0.00001;  //adjustable precision/*n is the number whose log is soughtb1 and b2 are two boundary values where b1 < n < b2l1 and l2 are the known logs of b1 and b2, respectively*/double rLog(double n, double b1, double b2, double l1, double l2) {  if( abs(b1 - b2) > precision ) {    gMean = sqrt( b1 * b2 );    aMean = ( l1 + l2 ) / 2;    if( n <= gMean ) rLog(n, b1, gMean, l1, aMean);    else rLog(m, gMean, b2, aMean, l2);  }  return aMean;}

Invoking, say, recLog(100, 10, 1000, 1, 3) gives 1.99999 or so. (Be wary of numberical errors)

Edited by - Graylien on June 28, 2001 9:59:41 PM

##### Share on other sites
thanx alot, graylien. that''s exactly what i was looking for.

To the vast majority of mankind, nothing is more agreeable than to escape the need for mental exertion... To most people, nothing is more troublesome than the effort of thinking.

• 10
• 18
• 14
• 18
• 15