Hi LucMeekes. Yes, you were right. I made a mistake. The problem happens when solving cnorm(-9). I tried your solution using erf() function. It returns the same value of cnorm, but the problem continues. I can't evaluate cnorm (x), when x<-9. This question is so important for me because I'm working with reliability applied to structures, and problems like this happens all the time.
I would like to point some possible solutions, but I don't know how to apply any of them.
The first one is: If the problem is related to the integral, I remember reading somewhere that they were scaling the function to be integrated before the integration, and undo the scaling after. If It's possible, I could write the function equivalent to cnorm(x) and solve the problem, but I don't know how to scale the funcion f(x)=dnorm(x,0,1) to be integrated from -∞ up to -9. The integration of the function on the limits mentioned is equivalent to the cnorm(-9).
The second is: I read in another place about wrinting function in C to be added to the mathcad library. I'm just thinking; if in the C programming language It's possible to define some variable that is able to handle numbers less than 10^-17, maybe It would be possible to solve the problem. Actually Idon't know if the problem is numbers less than 10^-17 or the limitation of the program related to working with numbers above 17 decimal places. But the goal is to define a variable in C language that is able to handle these numbers.
Thank you all for the help and the good discussion.
