Merge pull request #522 from sawyerbfuller/freqplot-improvements

Merge pull request #522 from sawyerbfuller/freqplot-improvements · python-control/python-control@73f65df

Original file line number	Diff line number	Diff line change
`@@ -174,7 +174,7 @@ def negate(sys):`
`174`	`174`	`>>> sys2 = negate(sys1) # Same as sys2 = -sys1.`
`175`	`175`
`176`	`176`	`"""`
`177`		`-return -sys;`
	`177`	`+return -sys`
`178`	`178`
`179`	`179`	`#! TODO: expand to allow sys2 default to work in MIMO case?`
`180`	`180`	`def feedback(sys1, sys2=1, sign=-1):`
`@@ -280,7 +280,7 @@ def append(*sys):`
`280`	`280`	`>>> sys = append(sys1, sys2)`
`281`	`281`
`282`	`282`	`"""`
`283`		`-s1 = sys[0]`
	`283`	`+s1 = ss._convert_to_statespace(sys[0])`
`284`	`284`	`for s in sys[1:]:`
`285`	`285`	`s1 = s1.append(s)`
`286`	`286`	`return s1`