When I planned to solved a real physical problem, I found there is not illustration about physical unit in the tutorial. Is it dimensionless? if not, how to specify the unit in the code, like meter or nanometer?
You have to convert your equation system to non-dimensional form.
There is no need to write the unit. You only deal with numbers and assume a unit for them (you can mention the unit as comments in your code). What ever parameters you have, choose compatible/matching units for them and the numbers in your result shall follow your input units.
Although It is a not good problem, Thank you!
