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As has been observed by Dr. Wolfgang Hintze if a,b and c are constant this coupled system has easily derived analytic solutions. In general, this site strongly encourages you to try to present your attempts and then focused clear guidance can be given. I post this as in this case this does not really require more than 'out of the box' functions. Perhaps it ...

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$Version (* "8.0 for Microsoft Windows (64-bit) (October 7, 2011)" *) Needs["VectorAnalysis`"] From the help file of VectorAnalysis you find the following useful commands CoordinateSystem (* Out[17]= Cartesian *) Coordinates[] (* These are not x, y, z but ... *) (* Out[20]= {Xx, Yy, Zz} *) Now you have Grad[Sin[Xx^2 + Yy^2]] (* Out[19]= {2 Xx ... 4 Mathematica v 10 data = {{59.666667, -37.333333, -4.232386, -12.291741}, {59.666667, \ -37., -4.232386, -12.291741}, {59.666667, -36.666667, -4.232386, \ -12.291741}, {52.666667, -42.666667, 18.513031, 4.27407}, {52.666667, -42.333333, 19.890438, 2.090569}, {52.666667, -42., 19.696155, 3.472964}}; Manipulate[ GeoGraphics[ ... 2 You can combine the best of both worlds: symbolic tensors and vectors on one hand, and explicit vectors on the other. Explicit vectors are necessary in most vector algebra operations, unless you want to rely heavily on UpValues defined for all those operations and all the symbols you're using. It's cleaner to let Mathematica's matrix algebra take over ... 0 v[t_] := Simplify[{0.95, 0.4, 0.35} - rsSpline[t]]; angle[t_] := VectorAngle[rsSpline'[t], v[t]] Note: (i) you should you SetDelayed (ii) the extra curly brackets in v[t] definition lead to the error->remove I have run the corrected code on a fresh session with no errors, e.g. Table[angle[j], {j, 0.1, 1, 0.1}] yielded {0.0887941, 0.0788714, ... 6 The option VectorPoints determines how many vector boxes there are. The plot domain is subdivided into a grid, whose grid points span the plot domain in each direction. Equal-size rectangular boxes surround each grid point so that the boxes are adjacent and tile the plot range (ignoring any padding). Here is a picture with VectorPoints -> 9 (the ... 1 Get intuition from this: Manipulate[ VectorPlot[{Sin[x], Cos[y]}, {x, -Pi, Pi}, {y, -Pi, Pi}, VectorScale -> {mysize, aratio}], {mysize, {Small, Medium, Large}}, {aratio, .1, 1, .1}] Here, mysize merely states how long a vector is (by gving a size of a bounding box). Here aratio ($0<aratio<1\$) merely states the ...

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As explained in Operators without Built-in Meanings, Subscript[x,y] is an operator, not a symbol. Subscript[x, 1] = Table[0, {i, 3}]; ?Subscript[x,1] Information::nomatch: No symbol matching Subscript[x,1] found. >> Thus, you cannot apply Part to it, because Part applies only to symbols. This is not associate with your nested For loops and can ...

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