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Calculus Wolfram Language Numerical Computation

Getting Value from Interpolating Function

Raunak Bardia

Raunak Bardia, University of Wisconsin-Madison

Posted 9 years ago

I solved a system of ordinary differental equations using NDsolve. Their plots look perfect. However, I am unable to extract the values from them at particular values. sol = NDSolve[{eqR1, eqR2, icR1, icR2, icm}, {R[t], m[t]}, {t, 0, 3010^(-5)}] Rbubble = R[t] /. sol mdot = m[t] /. sol Plot[{Rbubble/Ro}, {t, 0, 3010^(-5)}, PlotRange -> Automatic, AxesLabel -> {"Time (in s)", "Bubble Radius"}] Plot[mdot4PiRbubble^2, {t, 0, 3010^(-5)}, PlotRange -> Automatic, AxesLabel -> {"Time (in s)", "Mass Flux at interface"}] I am sure the solutions are correct because the plots look right. But I am unable to access Rbubble[0]. Please help!!!

I solved a system of ordinary differental equations using NDsolve. Their plots look perfect. However, I am unable to extract the values from them at particular values.

sol = NDSolve[{eqR1, eqR2, icR1, icR2, icm}, {R[t], m[t]}, {t, 0, 30*10^(-5)}]
Rbubble = R[t] /. sol
mdot = m[t] /. sol
Plot[{Rbubble/Ro}, {t, 0, 30*10^(-5)}, PlotRange -> Automatic, 
 AxesLabel -> {"Time (in s)", "Bubble Radius"}]
Plot[mdot*4*Pi*Rbubble^2, {t, 0, 30*10^(-5)}, PlotRange -> Automatic, 
 AxesLabel -> {"Time (in s)", "Mass Flux at interface"}]

I am sure the solutions are correct because the plots look right. But I am unable to access Rbubble[0].

Please help!!!

POSTED BY: Raunak Bardia

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David Keith

Posted 9 years ago

POSTED BY: David Keith

David Keith

Posted 9 years ago

Hi Raunak, It would be easier to respond if you had included the definitions for the equations. Then I could reproduce the work and display a syntax for doing what you want. But ---- Rhubble=R[t]/.sol produces an expression in t. When you plot that, Plot substitutes values for t and the plot works fine. But Rhubble is not a function; it is an expression. To evaluate it at t=0, you could use Rhubble/.t->0, which makes the replacement for t. Alternatively, you could make Rhubble a function by using Rhubble[t_]=R[t]/.sol. Now you would need to plot Rhubble[t], and Rhubble[0] would return a value. BTW -- I have used the variable names you gave. But it is better to begin user symbols with lower case. This is because Mathematica uses upper case for reserved symbols. Best, David