topic Re: How to plot a log normal distribution function in Mathcad

How to plot a log normal distribution function

ptc-3212469 — Thu, 03 May 2018 19:37:15 GMT

Dear all, I desire to plot a probability density function of log normal distribution: f(x)=(1/sqrt(2*pi)*beta*x)exp(-ln(x/M)^2/2*beta^2) on Mathcad but Mathcad announced a yellow message "this variable or function is not defined above". I do not know at which

Re: How to plot a log normal distribution function

StuartBruff — Tue, 06 Apr 2010 19:30:09 GMT

"Lam Bao" wrote:

Re: How to plot a log normal distribution function

ptc-3212469 — Thu, 08 Apr 2010 15:09:54 GMT

Hi Stuart, Thanks for your reply, I figured out. It was a typo error I did. A point automatically appeared when I typed the formule. However, I have another question relating to inverse trigonometric function asin, it seems to return a weird result. For example, I want to calculate sinus of 1.7 radian, I typed on the worksheet sin(1.7) and Mathcad return the value 0.992. To verify the radian of an angle whose sinus is 0.992, I typed asin(0.992) while expecting Mathcad will return 1.7 but no, it returns 1.444 instead. Could you tell me what's wrong with my handling? How I can solve it Thanks very much

Re: How to plot a log normal distribution function

RichardJ — Thu, 08 Apr 2010 15:21:42 GMT

asin returns the principle value. It has no way to know which of the infinite number of possible angles you had in mind. 1.7 radians is 97.4 deg. 1.44 radians is 82.6 deg. The sin of both angles is 0.992. Richard

Re: How to plot a log normal distribution function

ptc-3212469 — Thu, 08 Apr 2010 16:45:47 GMT

Thanks Richard, I understand, do you know how I can determine the range of the desired angle, for example, I only want Mathcad return the angle in the range of 0 to pi/2. Thank you very much

Re: How to plot a log normal distribution function

TomGutman — Thu, 08 Apr 2010 16:58:07 GMT

THe principle value for asin is between -pi/2 and pi/2. If you want between 0 and pi/2 you need to use arguments between zero and one. Note that in your original question you started with an angle larger than pi/2, and asin will never return such an angle.