Linked Questions

7 votes
3 answers
397 views

Why can't D[] be used in place here? [duplicate]

Possible Duplicate: General::ivar is not a valid variable when plotting - what actually causes this and how to avoid it? Beginner question: Why can't I use D[]...
Phantrast's user avatar
  • 293
6 votes
2 answers
2k views

Defining a function using Series? [duplicate]

Possible Duplicate: General::ivar is not a valid variable when plotting - what actually causes this and how to avoid it? I need to define a function using the output of series, i.e. ...
Pragabhava's user avatar
  • 1,619
0 votes
1 answer
1k views

Plot[ D[Sin[x]] ] and Evaluate[] [duplicate]

Why does t = 2 Pi; Plot[D[Sin[x],x], {x,0,t}] (* Plotting the derivative of Sin[x] *) not work, but ...
Daniel Beecham's user avatar
4 votes
3 answers
335 views

How to plot the derivative of an exponential function? [duplicate]

Plot[(1.8)^n, {n, 0.5, 10}] Works fine, but this derivative gives an error and does not plot. ...
CasperYC's user avatar
  • 1,642
0 votes
1 answer
656 views

Why is "1" not a valid variable? Why is there not a function plotted in the Plot function? [duplicate]

This is my code for playing this kind of stuff ...
kile's user avatar
  • 1,671
0 votes
1 answer
604 views

Mathematica issue with Plot, D and SetDelayed [duplicate]

I've tried to run the following code: f[x_] := 2 ArcTan[x] + ArcSin[2 x/(1 + x^2)]; Plot[D[f[x], x], {x, -4, 4}] Same with ...
m0nhawk's user avatar
  • 3,867
2 votes
1 answer
1k views

How to plot the derivative of NDSolve interpolation function? [duplicate]

So I got a question. Everytime I use a derivative of a function during plotting or ongoing evaluation, it seems Mathematica misunderstands me, and just derives a value (a constant) which always ...
M.Pow's user avatar
  • 65
1 vote
1 answer
663 views

General::ivar: is not a valid variable [duplicate]

...
zhk's user avatar
  • 12k
2 votes
2 answers
397 views

Derivative of Vectoral NDSolve Interpolated Function / Rule Solutions,/., and Vector NDSolve [duplicate]

I need to find the instantaneous phase and instantaneous frequency for a rotating system. I am having difficulty making the math work with interpolating functions. First, here is a problem without ...
Astor Florida's user avatar
0 votes
1 answer
643 views

Evaluating derivatives for use in solve [duplicate]

I need to evaluate the derivative of a function. My function looks like approx[vector_, x_] := Sum[vector[[n]]*Basis[n - 1, x], {n, 1, Length[vector]}] and I'm ...
user5866's user avatar
2 votes
2 answers
175 views

Mathematica code for Newton's Method doesn't work [duplicate]

I am trying to program Newton's Method in Mathematica to compute the roots of $f(x)=x^3-6x^2+11x-6$ using the Do command but my code gives a ...
user avatar
1 vote
1 answer
102 views

Ivar error with Fit inside Plot [duplicate]

I'm trying to plot this Plot[Fit[med,{1,x},x],{x,0,10}] Why this doesn't work? I find out that if I do ...
Kafkarudo's user avatar
  • 619
0 votes
2 answers
133 views

f'[x] not the same as D[f[x],x]?! (Problems with Plotting..) [duplicate]

I have a very strange problem I'm sure I haven't had before, but I'm new to Mathematica, so maybe I'm just tired and can't see the obvious. The Problem is, that for some reason Plot[] won't work with ...
Bleagle's user avatar
0 votes
1 answer
64 views

Evaluation of an Error function [duplicate]

How to evaluate df function in the following code sample? ...
Emad Raslan's user avatar
1 vote
0 answers
51 views

Why does Plot[D[x,x],{x,1,10}] throw error? [duplicate]

I am experiencing unexpected behavior from Plot and D, and I would like to understand why. If I try this: Plot[D[x,x],{x,1,10}]...
Yly's user avatar
  • 265

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