5.4) Multiple Variable Functions

A function which takes multiple input variables is no different to a single input function. You simply list the input variables after the function name, each separated by a comma. Here we will use the example of calculating the potential temperature, which requires the temperature and pressure as inputs. The equation for potential temperature (theta) is:

We can write a function to calculate theta given the temperature and pressure as inputs. Type the following into a file called temp_to_theta.pro:

Function temp_to_theta, t, p
; Function to convert T(K) and P(hPa) to theta
; using a reference pressure of 1000hPa
RoverCp=0.2896
p0=1000.
theta=t*(p0/p)^RoverCp
return, theta
END

We can the use the function to convert zero degrees Celsius (273.15K) at 900hPa to a potential temperature and place the result in the variable "theta" using:

theta = temp_to_theta(273.15, 900.)

You should get the answer "281.506".