Logarithm

Well thats actually quite strange. thermistor.comp use the log() function. I wonder why and even if it compiles?
github.com/LinuxCNC/linuxcnc/blob/master...omps/thermistor.comp .

The thermistor comp runs in userspace.

andypugh wrote: The thermistor comp runs in userspace.

Yes, I saw that but still it has no declaration in the header files for log(). The other user space components are quite liberal with standard #include files. Makes me wonder if log() should not be added to rtapi_math.h

I found a code. I will try it before post it. ASAP hope tomorow

I don't know if ther is a link but I found some people who get trouble to compile log in C with linux. They had to compiled the program with the -lm option. And it worked
like : www.unix.com/programming/63585-what-wrong-log-function-c.html
By the way, no clue what does it meens.

For simplicity, reliability and portability I think that "lincurve" is the best answer.
It was designed for exactly this sort of job, with inputs inside a well defined range.
We use the same approach extensively in my day job as it limits the computational overhead. And automatically limits outputs to sane values regardless of inputs.

I will work on lincurve, but i need some result. I use the easy way...
So : if somebody need a natural logarithm function in C, here it is


double log(double x){
int i=1;
double logx = 0 ;
double ty = (x-1)/(x+1) ;
double tty=0;
do
{
logx = logx + ty / i;
tty = ty ;
ty = (ty * ((x-1)/(x+1)) * ((x-1)/(x+1)));
i = i + 2 ;
}
while(tty - ty > 0.0000005 );
logx = 2*logx;
return logx;
}

log(2) will give 0.6314