I found the behavior weird, but I could find the eplanation, It seems that the function c2d recognize what method to use by reading the first letter of the first string. You have five methods 'zoh', 'foh', 'impulse', 'tustin', or 'matched'
Hd1=c2d(Hs,0.1,'tutsin') % or
Hd1=c2d(Hs,0.1,'t') % or
Hd1=c2d(Hs,0.1,'tall')
The three previous lines of code are using the same method 'tutsin', because the first letter is t
The following code use 'matched' method, because the first letter in the string 'method' is m, the second string 'tutsin' is ignored
Hd1=c2d(Hs,0.1,'method','tutsin')
