An example function (of one variable)

For example, you have seen that IDL uses radians. You might want to convert from radians back to degrees. You can do that using,

a_rad=0.5 
a_deg=a_rad*180./!pi

but that's not very neat. If you use this a lot you will have to type a lot and maybe make mistakes.

We can define a small program that does this for us. Open a file called rad_to_deg.pro

Put the lines below in it.

Function rad_to_deg,input_rad

;Function to convert radians to degrees

output_deg=input_rad*180./!pi
return,output_deg

end

Note that the ``;'' symbol is a comment and ignored by IDL and you should always put a comment at the start of a program saying what it does.

We can use our program by for example typing,

.compile rad_to_deg
degrees=rad_to_deg(!pi/2.)
print,degrees

IDL puts ``!pi/2.'' into the function (the input parameter), and converts it to degress and outputs this (the returned variable).