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Mar
29
comment Fitting data without an equation
My understanding was that the data aren't necessarily given by a known function...
Mar
29
comment Fitting data without an equation
The simplest fit is linear interpolation between data points. And that is done by using the following magical incantation: ListPlot[H, Joined -> True]. Do you want anything fancier that this? If so, could you describe it in more detail?
Mar
28
comment How to make a defined symbol stay in symbol form?
You probably forgot to copy the line SetAttributes[myList, HoldAll]
Mar
28
comment How to make a defined symbol stay in symbol form?
I didn't get what your goal was initially, but I think now the DumpSave should work.
Mar
28
comment Sum and NSum gives different solutions
@whuber One should however be careful not to overstate the differences between Sum and NSum. According to the documentation for Sum (under "Properties"): Applying N to an unevaluated sum effectively uses NSum
Mar
27
comment how to generate functions with changing array size?
Right, I overlooked the lower bound. It's corrected now. Also, I think I added what you meant in terms of the f[i,x], but I'm not sure if you wanted them to remain symbolic or see their values as it appears in my answer.
Mar
27
comment Click on a curve to start Manipulating another function
Are you perhaps trying to do something similar to my answer here?
Mar
26
comment How can I name “a[[i]]” the parts of Table “a”? Or how to make Table “a” grow inside FindMinimum?
(+1) that's the cleanest solution (I think Mathematica used to be unable to do this, but it got cleverer...)
Mar
26
comment Adding and subtracting from elements in a list
@Mr.Wizard Sure, I just didn't want to copy you (already upvoted your answer, of course)... and maybe Outer is helpful because you can generalize it to construct other matrices.
Mar
25
comment Why does simplification in Mathematica depend on variable names
I attempted an explanation of this phenomenon in this related post
Mar
25
comment Fortran kind of matrix creation
Are you sure you want the inner If in terms of i, j - and not in terms of ix, iy, jx, jy? The latter seems more natural and would probably make it easier to write this in a more Mathematica friendly way.
Mar
25
comment NDSolve does not respond
@OleksandrR. I don't know if this answers your question, but the reason FindRoot or something like it comes into play is this: the first-order DAE is equivalent to a second-order differential equation obtained by taking $d/dt$ on both sides. Since the order increased, we need an additional initial condition (for Vo'[0]). But the latter is not at our disposal because the original DAE fixes it via the value of V which got killed in the $d/dt$. This is where FindRoot comes in to determine what the correct Vo'[0] is. Then the 2nd order diff. eqn. can be solved as usual.
Mar
25
comment How to simplify expressions containing derivatives
But then the title of the question should be different.
Mar
25
comment How to simplify expressions containing derivatives
You should spend some time writing a small example in valid Mathematica code so that we can see what your starting point is. Otherwise we'd have to waste time guessing wether some or all of the f, g, h are defined or not, whether x is the independent variable, etc.
Mar
24
comment Plotting a large number of data points
@cormullion I looked up the guideline on downvoting, and near the bottom it mentions that it should be used in extreme cases only. This question seems quite innocent to me.
Mar
24
comment Finding Limits in several variables
I see - and had a look at the paper you referenced. Seems like Maple wasn't able to do that limit either...
Mar
23
comment How to generate a matrix group?
That's better than using Tuples - the scaling is dramatically improved.
Mar
23
comment How to apply a function to a list of tuples
The MapAt solution works in version 9, but in version 8 it throws an error "Position specification {1;;All,2} ...is not an integer or a list of integers"
Mar
22
comment How to generate a matrix group?
OK, so these are three orthogonal matrices with determinant 1. That means they can be generated by $n(n-1)/2 = 21$ parameters. What remains to do is to find the subgroup to which they belong.
Mar
22
comment How to generate a matrix group?
@whuber Brute force methods without crashes aren't true brute force... But I'll add some safety remarks, I think.