Logarithm

Hy
I feel dumb
I try to install this code as compoment file .comp:

float thermistor2temperature(float R) {
float T;
if (R<=0)
R=0.001; // avoid log(0)
T = 1.0/ ( 1.0/T0 + (1.0/ * log(R/R0) );
return T;

I do include #include <rtapi_math.h>

During compilation i get error : implicit declaration of function 'log'

What am I doing wrong???
thanks

@Yann,

#include <rtapi_math.h>
log(10);

Will work.

You have to check your formula.

Thanks for your answer
But still don't want corporate. log( anything) always return implicit declaration of fonction 'log'
It's really weird and i don't know in which direction to look to find a solution

What happens if you use doubles?

I suspect a type error

I thought that also. And I try it again.
I even try with with a log alone like
double R = log(133)
but it return alway the same error

I'm a bit lost
Do you have an idea were can i find a log code function. I could write it but my mathematique skill are a bit poor.

You can test with

Hmm, log() is not included in rtapi_math.h github.com/LinuxCNC/linuxcnc/blob/master/src/rtapi/rtapi_math.h

I would search for the C code in the GCC compiler for the log function and add it to my component.

Or try and add it to the header file....

thanks for your answers

I will work on that

I using linuxcnc to drive a reprap. I'm following and adapting the work of this guy.
www.anderswallin.net/2012/12/temperature-pid-control-part-deux/

Using hal encoder with NTC resistor and ne555 chip to control PID and pwmgen.
Thermistor change a frequency read by linuxcnc.....regulate extruder and hotbed temperature
To calcul the temperature with the frequency I need a log

I will work on the direction you give. And come back with the result
thanks