# Questions tagged [evaluation]

Questions about how Mathematica evaluates expressions, tracing evaluation (Trace*), handling expressions in unevaluated form (Hold*, Unevaluated), nonstandard evaluation, etc.

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### How to “Hold” variables assigned value inside DSolve?

Consider the following ODE: a = 0.8; b = 8; v = DSolveValue[{ u[x] == a*(b* u'[x] + u''[x]), u[4.925] == 4, u'[4.925] == 0.625 }, u[x], x] which gives ...
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### Evaluation order of multi-argument function and why is () sometimes equivalent to Evaluate[]?

So this question has two parts: 1) How can the order of evaluation of a multi-argument function be determined? and 2) Why does () seem to be equivalent to Evaluate[] in some cases? I was plotting a ...
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### Why can't I evaluate this integral and obtain a closed-form solution?

I have the following spherical density distribution: $\rho(x, z) = \frac{1}{\sqrt{x^2 + z^2}\left(1+\sqrt{x^2+z^2}\right)^2}$ which I have broken into a "line of sight" dimension $z$ and a &...
71 views

### Still having trouble evaluating expressions (involving Log this time)

I'm trying to get some old Mathematica code working on MMA 12. I found the code at this link. Here's the relevant code: ...
26 views

### Evaluation time of If[] conditionals taking too long [closed]

I have a simulation to run, and the whole script was written by somebody else (I think over 10 years ago) so I know it works perfectly. However, when I try to run in myself, there is an input, with ...
29 views

### How does Mathematica evaluate sums where the upper limit of the index is not an integer?

I am interested in the way Mathematica evaluates sums where the upper limit of the index is not an integer - i.e., sums that are some sense mathematically meaningless. For example: ...
96 views

### Can you transcribe this mathematica expression into a formula or pseudocode?

I want to understand the mathematca formula A282720 The description says Number of nonzero terms in first n rows of the base-2 generalized Pascal triangle P_2 (But ...
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### How to asign well numerical values efficiently before to plot?

A problem is presented when the substitution of the numerical values for this function ...
78 views

### Ignore Null when summing elements of a list, but return Null if all elements are Null

Let's say I have two different lists for which I want to compute the total list1 = {1, Null, 2, Null} list2 = {Null, Null, Null, Null} For list1, I want the total ...
24 views

### How to DumpSave previously assigned symbols

I'm trying to DumpSave[] some variables based on their name string. To define them, I'm using ...
41 views

### Which Method is used during the processing of Sum Function?

I am trying to find out which Method is used while evaluating the following function: Sum[1/((n^2)), {n, 1, Infinity}] Any help would be greatly appreciated. A ...
111 views

### How can I use Compile to Evalaute a trace of a sympolic Matrix?

I would like to evaluate a trace of a matrix of size 4Wn×4Wn at different point (x,y). with <...
221 views

### HoldForm does not prevent evaluation

I'm still relatively new here, and I'm not a native speaker. I hope, I don't make any obvious mistakes when asking this question. For instance, I simply had no idea how to title it accurately. I'm ...
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### Evaluation order and Tables - Errors when using Evaluate@Table

following this question of mine Conditional PlotStyle, I ran into another problem. I fear it has to do with evaluation orders, as for example described in Table and Evaluation Order, but I am totally ...
44 views

### The number 1 evaluates inside HoldForm sometimes

If I run the following code: ...