Skip to main content

calculus and analysis - Interpolating an Antiderivative



I'd like to be able to make InterpolatingFunctions for antiderivatives of functions that can't be integrated symbolically. However, the following code returns several error messages:


FunctionInterpolation[Integrate[Sqrt[1 + x^3], {x, 0, t}], {t, 0, 10}]

Here are the messages:



Thread::tdlen: "Objects of unequal length in {-1.25,-0.416667,0.416667,1.25}^{} cannot be combined. "


Thread::tdlen: "Objects of unequal length in {0.223144 +3.14159\ I,-0.875469+3.14159\ I,-0.875469,0.223144}\ {}\n cannot be combined. "


Thread::tdlen: "Objects of unequal length in {-1.25,-0.416667,0.416667,1.25}\ {} cannot be combined."


General::stop: "Further output of Thread::tlden will be suppressed during this calculation."


FunctionInterpolation::nreal: Near t = 1.25`, the function did not evaluate to a real number.



FunctionInterpolation::nreal: Near t = 1.3277777777777777`, the function did not evaluate to a real number.



What's going on? Is there a simple way to make this work? Changing Integrate to NIntegrate doesn't help, though the error messages are different:



NIntegrate::nlim: x = t is not a valid limit of integration.


NIntegrate::nlim: x = t is not a valid limit of integration.


NIntegrate::nlim: x = t is not a valid limit of integration.


General::stop: "Further output of NIntegrate::nlim will be suppressed during this calculation. "




Answer




Use NDSolve


antiD = NDSolveValue[{f'[x] == Sqrt[1 + x^3], f[0] == 0}, f, {x, 0, 10}]

Example usage:


Plot[antiD[x], {x, 0, 10}]

Mathematica graphics




Alternatively...


This works because this function can be antidifferentiated (by Mathematica).



antiD = FunctionInterpolation[
Evaluate @ Integrate[Sqrt[1 + x^3], {x, 0, t}, Assumptions -> 0 < t < 10],
{t, 0, 10}]

or...


integral[t_?NumericQ] := NIntegrate[Sqrt[1 + x^3], {x, 0, t}];
FunctionInterpolation[integral[t], {t, 0, 10}]

FunctionInterpolation evaluated its argument on a symbolic t. The pattern test ?NumericQ prevents evaluation of NIntegrate until an actual number is substituted for t. See also What are the most common pitfalls awaiting new users?. Note also that this way does many evaluations of NIntegrate, whereas the NDSolve method does just one integration.


Comments

Popular posts from this blog

plotting - How to draw lines between specified dots on ListPlot?

I would like to create a plot where I have unconnected dots and some connected. So far, I have figured out how to draw the dots. My code is the following: ListPlot[{{1, 1}, {2, 2}, {3, 3}, {4, 4}, {1, 4}, {2, 5}, {3, 6}, {4, 7}, {1, 7}, {2, 8}, {3, 9}, {4, 10}, {1, 10}, {2, 11}, {3, 12}, {4,13}, {2.5, 7}}, Ticks -> {{1, 2, 3, 4}, None}, AxesStyle -> Thin, TicksStyle -> Directive[Black, Bold, 12], Mesh -> Full] I have thought using ListLinePlot command, but I don't know how to specify to the command to draw only selected lines between the dots. Do have any suggestions/hints on how to do that? Thank you. Answer One possibility would be to use Epilog with Line : ListPlot[ {{1, 1}, {2, 2}, {3, 3}, {4, 4}, {1, 4}, {2, 5}, {3, 6}, {4, 7}, {1, 7}, {2, 8}, {3, 9}, {4, 10}, {1, 10}, {2, 11}, {3, 12}, {4, 13}, {2.5, 7}}, Ticks -> {{1, 2, 3, 4}, None}, AxesStyle -> Thin, TicksStyle -> Directive[Black, Bold, 12], Mesh -> Full, Epilog -> { Line[ ...

dynamic - How can I make a clickable ArrayPlot that returns input?

I would like to create a dynamic ArrayPlot so that the rectangles, when clicked, provide the input. Can I use ArrayPlot for this? Or is there something else I should have to use? Answer ArrayPlot is much more than just a simple array like Grid : it represents a ranged 2D dataset, and its visualization can be finetuned by options like DataReversed and DataRange . These features make it quite complicated to reproduce the same layout and order with Grid . Here I offer AnnotatedArrayPlot which comes in handy when your dataset is more than just a flat 2D array. The dynamic interface allows highlighting individual cells and possibly interacting with them. AnnotatedArrayPlot works the same way as ArrayPlot and accepts the same options plus Enabled , HighlightCoordinates , HighlightStyle and HighlightElementFunction . data = {{Missing["HasSomeMoreData"], GrayLevel[ 1], {RGBColor[0, 1, 1], RGBColor[0, 0, 1], GrayLevel[1]}, RGBColor[0, 1, 0]}, {GrayLevel[0], GrayLevel...

list manipulation - Selecting multiple columns from a matrix?

Sample data: data = { {{2013, 1, 1}, 24.13, 167.67, 231.82}, {{2013, 1, 2}, 32.15, 170.92, 225.99}, {{2013, 1, 3}, 35.43, 172.68, 221.67}, {{2013, 1, 4}, 36.73, 173.05, 218.32}, {{2013, 1, 5}, 58.19, 165.96, 197.05}, {{2013, 1, 6}, 69.99, 163.50, 187.52}, {{2013, 1, 7}, 71.37, 154.21, 175.58}, {{2013, 1, 8}, 72.51, 149.66, 163.25}}; I want a DateListPlot with three graphs, so for a matrix formed by columns 1 and 2, one for columns 1 and 3, and 1 for columns 1 and 4. At the moment I'm using this code: data2 = Transpose[{data[[All, 1]], data[[All, 2]]}]; data3 = Transpose[{data[[All, 1]], data[[All, 3]]}]; data4 = Transpose[{data[[All, 1]], data[[All, 4]]}]; DateListPlot[{data2, data3, data4}, Joined -> True, Filling -> {3 -> {1}}] but I have a hunch that this can be done more efficiently. I don't like the Transpose s in particular. Any ideas? edit (for extra credit) What if I need to multiply the second column by 2, which in my solution is simp...