Using command-line arguments

From the last run of our code, we can see that 500 iterations is not enough to get to a steady state (a state where the difference in temperature does not vary too much, i.e. delta<tolerance). Now, if we want to change the number of iterations we would need to modify niter in the code, and compile it again. What if we want to change the number of rows and columns in our grid to have more precision, or if we want to see the evolution of the temperature at a different point (iout,jout)? The answer would be the same, modify the code and compile it again!

No need to say that this would be very tedious and inefficient. A better scenario would be if we can pass the desired configuration values to our binary when it is called at the command line. The Chapel mechanism for this is the use of config variables. When a variable is declared with the config keyword, in addition to var or const, like this:

config const niter = 500;             //number of iterations

$ chpl baseSolver.chpl -o baseSolver    # using the default value 500
$ ./baseSolver --niter=3000             # passing another value from the command line

Temperature at iteration 0: 25.0
Temperature at iteration 20: 2.0859
...
Temperature at iteration 2980: 0.793969
Temperature at iteration 3000: 0.793947
Final temperature at the desired position after 3000 iterations is: 0.793947
The greatest difference in temperatures between the last two iterations was: 0.00142546

Exercise “Basic.4”

Make rows, cols, nout, iout, jout, tolerance configurable variables, and test the code simulating different configurations. What can you conclude about the performance of the code.