If you are interested in computing the original PDSI and you are also using MATLAB, you can take a look on this option: http://onlinelibrary.wiley.com/store/10.1002/wrcr.20342/asset/wrcr20342.pdf?v=1&t=igyif2bj&s=c31be51b74be21ba5269be9b486578938cce953a
Personally, I am not familiar with this tool, since I am using Python for writing a code to compute the self-calibrating PDSI (sc_PDSI) instead.
Also, there is a program that runs in Windows made by Nathan Wells and others. You can download it here: http://greenleaf.unl.edu/downloads/
If you are able to compile C++ programs, there is also available a code to compute the sc_PDSI at https://github.com/cszang/pdsi/blob/master/exec/scpdsi.cpp
If you are interested in computing the original PDSI and you are also using MATLAB, you can take a look on this option: http://onlinelibrary.wiley.com/store/10.1002/wrcr.20342/asset/wrcr20342.pdf?v=1&t=igyif2bj&s=c31be51b74be21ba5269be9b486578938cce953a
Personally, I am not familiar with this tool, since I am using Python for writing a code to compute the self-calibrating PDSI (sc_PDSI) instead.
Also, there is a program that runs in Windows made by Nathan Wells and others. You can download it here: http://greenleaf.unl.edu/downloads/
If you are able to compile C++ programs, there is also available a code to compute the sc_PDSI at https://github.com/cszang/pdsi/blob/master/exec/scpdsi.cpp