The file physics constains results for $\pi^+$ meson as input and
$\pi^+$ meson as
output. physics1 is for $\pi^-$ to $\pi^-$.
Arguments
source
Weisberg, H., Beier, H., Brody, H., Patton, R., Raychaudhari, K., Takeda, H.,
Thern, R. and Van Berg, R. (1978).
s-dependence of proton fragmentation by hadrons. II. Incident laboratory
momenta, 30--250 GeV/c. Physics Review D, 17, 2875--2887.
References
Weisberg, S. (2005). Applied Linear Regression, 3rd edition. New York: Wiley, Section 5.1.1.