In article <5820dc553954e44fa1a36c78323ad148a4085...@uxcn10-6.uoa.auckland.ac.nz>, Steve Shipway <s.ship...@auckland.ac.nz> wrote: > > Example: 3*x^2 > > I thought this would be in rpn: 3,x,2,EXP,* > > However, rrdtool is complaining "ERROR: RPN final stack size != 1" > > EXP is the reverse of the natural log, sometimes called 'antilog' ; IE, e^X, > NOT X squared. It also does not take a second argument as it always uses e > (2.71828etc). Thus, your RPN above ens up with two items in the stack (3, and > x(e^2)) > > If you want to raise X to the power of Y, then there is no single RPN > function to do it. Instead, you need to work through logarithms. > > e^( log(x) + log(y) ) == x * y ( a long way to go about it ) > > e^( log(x) * y ) == x ^ y > > Or, in RPN, > > x,LOG,y,*,EXP > > I agree it would be helpful to have a new command (eg. 'x,y,POW') to do this > in a single operation, but nobody has submitted it yet...
Of course if you just want the square, replace x^2 with x*x to give 3*x*x: 3,x,DUP,*,* Cheers Tony -- Tony Mountifield Work: t...@softins.co.uk - http://www.softins.co.uk Play: t...@mountifield.org - http://tony.mountifield.org _______________________________________________ rrd-users mailing list rrd-users@lists.oetiker.ch https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
