wolfram-mathematica

问题 For example, I want mma to expand out the following differential operator (1+d/dx+x*d2/dy2)^2*(1+y*d/dy)^2 I found Nest is not good enough to do this sort of things. 回答1: A bit dated, but see http://library.wolfram.com/infocenter/Conferences/325/ The section "Some noncommutative algebraic manipulation" gives a few ways to go about this. The first example, defining a function called differentialOperate, is probably best suited for your purposes. ---edit, reedited--- Here is the code I use.

问题 Merged with Syntax Coloring In Mathematica. Is there a trick to assign a specific color to "user-defined" function such as "function" below : function[x_]:=x^3 Thanks to Mr.Wizard we are able to color all user defined symbols ( Syntax Coloring In Mathematica) Would there be a way to refine the solution to have different colors for Functions symbols, Variables symbols & Options symbols ? EDIT : Image for Simon 来源： https://stackoverflow.com/questions/6165977/user-defined-function-coloring-in

问题 I created a random double precision value in Matlab by x = rand(1,1); then display all possible digits of x by vpa(x,100) and obtain: 0.2238119394911369 7971853298440692014992237091064453125 I save x to a .mat file, and import it into Mathematica, and then convert it: y = N[FromDigits[RealDigits[x]],100] and obtain: 0.2238119394911369 0000 Then go back to Matlab and use (copy and paste all the Mathematica digits to Matlab): vpa(0.22381193949113690000,100) and obtain: 0.22381193949113689

问题 I have imported a csv file into a list with this stmt: data1 = Take[Import["D:\\_reports\\optim_5_60_b_2.csv", "CSV"], 5] Which gives: {{178, 8, 9, 1}, {152, 2, 8, 1}, {378, 8, 9, 2}, {343, 3, 7.5`, 2}, {143, 3, 7.5`, 1}} I would like to create a plot where the x-axis is based on the first field: 178,152,378,343,143,373,743,352 And the plot creates a line for each subsequent field, so the 2nd field is: 8,2,8,3,3,3,3,2 This would be the first line on the y-axis, the other y-axis values would

问题 I have a population of objects (each of which is described by a sequence of real numbers), and I'd like to find the "distance" between a single test object and the median of the population. I believe that I can use the MultivariateStatistics package to characterize my population, and then either SpatialMedian[] or SimplexMedian[] to find the "center." My goal is to find the distance between a test object and this median. I gather that a simple Euclidean distance would be incorrect, because I

问题 I have an expression which involves x1,x2,...,x100, I also have a list lst with 100 elements, how to apply the rule to this expression to achieve something like the following: exp/.{x1->lst[[1]],x2->lst[[2]],...,x100->lst[[100]]} Thanks! 回答1: exp /. Table[Symbol["x" <> ToString[i]] -> lst[[i]], {i, 1, 100}] So you don't need to write X1,X2, ... X100 回答2: You can use Thread to apply the rules to each pair of expressions: Thread[{a, b, c} -> {1, 2, 3}] 回答3: It is much simpler and more

问题 Given that g is a graphics object with primitives such as Line s and Polygon s, how do you remove some of them? To add more primitives to an existing graphics object we can use Show , for instance: Show[g, g2] where g2 is another graphics object with other primitives. But how do you remove unwanted primitive objects? Take a look at the following ListPlot3D[{{0, 0, 1}, {1, 0, 0}, {0, 1, 0}, {1, 1, 0}}, Mesh -> {1, 1}] Now, for the input form: InputForm[ ListPlot3D[{{0, 0, 1}, {1, 0, 0}, {0, 1,

问题 Is it possible that when I Plot a function in Mathematica, it will automatically put near it it's equation(i.e. y = 2x) or even some other text? At first glance I don't find any option for it, but if there is one I'd like to know. Thanks 回答1: Using Mathematica 6 or higher, I often use Tooltip to help me identify plot curves: Plot[Tooltip[Sin[x]], {x, 0, 8 Pi}] Alas, this is only useful when using the graph interactively since you must hover the mouse cursor over the curve. It doesn't work so

问题 Is there a better way to count the number of elements for which the predicate function is true, other than this: PredCount[lst_, pred_] := Length@Select[lst, pred]; I'm asking because it seems inefficient to construct a subset of lst with Select[] , and because Count[] only works with patterns. In my use case, the function PredCount is called many times with a large lst . 回答1: You can often do this by turning your predicate into a pattern with a condition. For example: Count[list, x_/;x>5]

问题 I tried ColorConvert[img, "Grayscale"] to convert the RGB to Graylevel . I am wondering the detailed calculation by mathematica.. Gray level= square(R^2+G^2+B^2)? or something else? 回答1: We can obtain the exact values used by mathematica by making up a 3 pixel image with pure red,green,blue and converting it: lvec = First@ ImageData[ ColorConvert[Image[{{{1, 0, 0}, {0, 1, 0}, {0, 0, 1}}}], "GrayScale"]] {0.299, 0.587, 0.114} Note these are the "Rec. 601 luna coefficients" per http://en