User Behzad Navidi asked if implementing SPI would require significant additional changes to the code.
Answer:
Computing the SPI will only require a small
change in the code. The water balance D=P-E will no longer be necessary
and can be replaced with D=P. This would mean that the standardization
of the variable later could be made with the gamma function, but I
don't see a reason why the currently implemented log-logistic won't work.
That would require creating a new function spi.m that would be similar
to spei.m only with the small change described above. Definitely worth
doing.
User Behzad Navidi asked if implementing SPI would require significant additional changes to the code.
Answer: