# Summation of Bode Plots

Posted 9 years ago
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 Can anyone explain how I can create a plot of the summation of two or more bode plots. I have created 3 bode plots named G1, G2, and G3. I would like to create a bode plot called G4 which is the Magnitude of the previous 3 summed, and the Phase of the previous 3 summed. Each Bode plot was created using the following notation: G1 = TransferFunctionModel[{"my function"},s]; G2 = ... G3 = ... Somehow I would like G4 to be the bode plot of G1+G2+G3.... but this notation is clearly incorrect.Then I did BodePlot[{G1,G2,G3,G4},{10,10^(10)}] Can someone please advise!!! Thank you!!
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Posted 9 years ago
 missed the "s" sorry.
Posted 9 years ago
 I have mathematica 8 and it doesn't seem to recognize the SystemModelSeriesConnect function. Am I missing something obvious?
Posted 9 years ago
 That sounds right to me. I just did not know the syntax for doing what I wanted to do. Appreciate the help!!!!
Posted 9 years ago
 Hi DJ,It depends on what you mean by sum. On a Bode plot gains are in dB, so summing is equivalent to multiplication of gains, which is a series connection for transfer functions. (Or multiplication in the s-domain.) Such multiplication also sums phase response. Below tf1 has DC gain 1 and a single pole at -10; tf2 has gain 2 and a pole at -1000; tfSum is the series connection. tf1 = TransferFunctionModel[{{{{}}}, {{{-10}}}, {{1 10}}}, s] tf2 = TransferFunctionModel[{{{{}}}, {{{-1000}}}, {{2 1000}}}, s] tfSum = SystemsModelSeriesConnect[tf1, tf2] BodePlot[{tf1, tf2, tfSum}, PlotLegends -> {"TF1", "TF2", "Sum"}] 
Posted 9 years ago