Math Tips

• How can I calculate the local standard deviation or variance in an image?
• How can I determine if a point is inside a polygon?
• What's up with the IDL FFT function? I don't get the same values as my FORTRAN FFT function.
• How do I obtain either a binary or hexadecimal representation of a number?
• I want a more flexible curve fitting program. Can you help?
• How can I calculate the logarithm base 2 of a vector in IDL?
• How do you check for NANs in an array?
• How do I test for NANs in my programs?
• How do I calculate the center of mass of a 2D or 3D array?
• What is the most efficient way to rotate a volume?
• Help! The sky is falling with the way this number is represented in IDL!
• I'd like to fit a polygon about a set of points. How do I do that?
• How do I add two vectors that have NANs in them?
• Do these floating underflow errors mean anything!?
• Is there a fast way to get the sum of the diagonals of an array?
• How do I get a Gaussian distributon of numbers with a specified mean and sigma?
• Whoa! Did the behavior of ATAN change recently?
• I'm having some trouble getting random points on the surface of a sphere. Can you help?
• Histogram: On the Razor's Edge. A fable of interest to all computer users.
• Are the Sigma and Chi-Square parameters in CURVEFIT screwy? Or am I just losing my mind?
• Yikes! My double precision value is not very precise.
• How can I interpolate a value on a regular grid?
• I'm having trouble calculating derivatives in IDL. Can you help?
• Is there a easy way to interpolate bad data points in a vector?
• Is there a better way to represent missing data then using large numbers?
• How is a floating point number really stored in IDL?
• Do you know any interesting facts about exponential operations in IDL?
• When does one plus one equal one in IDL?
• Is it possible to interpolate without changing the mean value of the original data?
• What is the meaning of the value returned by the “Chi Square” keyword?
• When is zero less than a negative number?