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## probability distribution function (normal distribution)

version 1.2 (1.63 KB) by

This function calculates the probability under the normal distribution curve

Updated

This function calculates the probability under the normal distribution curve, plots the graph and the area calculated.

%Normaldistribution
%
% calculating the area under a normal distribution curve
% from -ve infinity upto point x.
%
% Input:
% x : point on the normal distribution curve
% mean : mean of the normal distribution curve
% sigma : standard deviation of the normal distribution curve
% (hint: normal dist mean=0, sigma=1)
% plotting: Plot the calculated area if plotting = 1
% Output: area under the curve.
%
% Example:
% x=[-20:20] % your data points
% sigma=length(x)/2/3.5 % PDF width is 3.5 sigma
% mean=0 % mean between -20 and 20
% normaldistribution(0, mean, sigma,1) % Calculate area from -inf to 0
%
%
% Author:
% Sherif Omran
% University and university hospital of Zurich
% Date: May 2009
% Part of my phd thesis:
% email: sherif.omran@gmx.de
%-------------------------------------------------------------------------%

ss grandite

### ss grandite (view profile)

This is a cdf (cumulative density function), actually. If you need better than 2 decimel places of accuracy, you can increase the resolution manually.

cabrego

### cabrego (view profile)

The shaded area in the function input below appears to be a little buggy, is that correct?

normaldistribution(.8686,1.02,.0829,1)

Sherif Omran

### Sherif Omran (view profile)

I made an example to use my code. Assume you have a distribution from -20 to 20 with mean at 0, and you want to calculate the area from -inf to 0

Example:
x=[-20:20] % your data points
sigma=length(x)/2/3.5 % standard div. normal dist. with is 3.5
mean=0 % mean of distribution
normaldistribution(0, mean, sigma,1)