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Student Support Forum: 'combine two functions using if or piecewise' topicStudent Support Forum > General > "combine two functions using if or piecewise"

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Author Comment/Response
Lyna
05/23/12 04:08am

Hello all,

i solved two couples of differential equations
sol[]:= NDSolve {x[t]= , y[t]= }
sol1[]:= NDSolve{x1[t]= , y1[t]= }

after some treatement and intermediate equations

ss= sol[[]]
ss1=sol[[]]

i plot the result of each equation :

pp1 = Plot[Evaluate[y[t] /. ss], {t, 0, 7}, AxesLabel -> {y, t}, PlotRange -> {{-10, 10}, {-1, 15}, {1, 7}}];


i want that :y[t] is active until it reachs y[t]=4 then y1[t] is active until y1[t]=0

my problem is when i want to combine these different results
i used :

If[y[t] < 4, Plot[Evaluate[y[t] /. ss], {t, 0, 7}], If[y[t] >= 0, Plot[Evaluate[y1[t] /. ss1], {t, 0, 7}]]]

but i dont have any result;
tried also piecewise

Do[
Plot[Piecewise[{{Evaluate[y[t] /. ss], {y'[t]>0,
y[t] < 4}}, {Evaluate[y1[t] /. ss1], {y'[t] < 0,
y1[t] > 0}}}], {t, 0, 20}],
{i, 1, 5}]

Any suggestions?

Regards

and i have errors that it dosn't accept the replace all, .

i verified the conditions but i don't understund why i don't have result
x

Attachment: automate hybride.nb, URL: ,

Subject (listing for 'combine two functions using if or piecewise')
Author Date Posted
combine two functions using if or piecewise Lyna 05/23/12 04:08am
Re: combine two functions using if or piecewise Michael 05/23/12 12:04pm
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