Why this code doesn't work? Can anyone help me?
s = {1, 2, 3};
f[x_, s_] :=
Piecewise[
Table[{x + i, s[[i]] <= x <= s[[ i + 1]]}, {i, Length[s[1]] - 1}]]
Manipulate[Plot[f[x, s], {x, 0, 3}], {s[[1]], 0, 3}]
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$\begingroup$ Read the error message: {s[[1]], 0, 3} is not a variable specification. Do you mean:Manipulate[Plot[f[x, var], {x, 0, 3}], {var, s}] $\endgroup$– Daniel HuberCommented Feb 16, 2022 at 16:23
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$\begingroup$ I wanna change the value of s[[i]] with manipulate $\endgroup$– Tony StackCommented Feb 16, 2022 at 16:29
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$\begingroup$ Then "i" is the variable? $\endgroup$– Daniel HuberCommented Feb 16, 2022 at 16:34
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$\begingroup$ for example for i=1 i have s[[1]]=1 (in this case) but, using manipulate, i wanna change the value of s[[i]] $\endgroup$– Tony StackCommented Feb 16, 2022 at 16:36
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1$\begingroup$ You must do this inside Manipulate. The variable for manipulate must be a simple like e.g. "i" variable, not an array member. $\endgroup$– Daniel HuberCommented Feb 16, 2022 at 16:44
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3 Answers
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Clear["Global`*"]
s = {1, 2, 3};
f[x_] = Piecewise[
Table[{x + i, s[[i]] <= x <= s[[i + 1]]}, {i, Length[s] - 1}]]
Plot[f[x], {x, 0, 3}]
EDIT:
Clear[f]
f[x_, s_] :=
Piecewise[
Table[{x + i, s[[i]] <= x <= s[[i + 1]]}, {i, Length[s] - 1}]]
Manipulate[
s = s0 + {1, 2, 3};
Column[{StringForm["`` = ``", HoldForm[f[x, s]], f[x, s]],
Plot[f[x, s], {x, s0, s0 + 3},
PlotRange -> {{0, 6}, {0, 9}},
PlotRangePadding -> Scaled[0.01],
ImageSize -> Medium]}],
{{s0, 0}, 0, 3, 0.05, Appearance -> "Labeled"}]
answered Feb 16, 2022 at 16:24
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$\begingroup$ thanks but i wanna change the intervals with manipulate $\endgroup$ Commented Feb 16, 2022 at 16:34
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$\begingroup$ Then you need to add something to the definition of
fthat varies and can be manipulated. $\endgroup$ Commented Feb 16, 2022 at 16:36 -
$\begingroup$ yes, but why my code is wrong? $\endgroup$ Commented Feb 16, 2022 at 16:37
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$\begingroup$ Because you gave
sa fixed value and once defined, the definition offdoes not change. You would need to make the definition ofsvariable. Alternatively, makefdependent on another variable other thanx$\endgroup$ Commented Feb 16, 2022 at 16:41 -
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I'm making some guesses about what you want, but here's a line of thinking...
First off, your function f doesn't really depend on x, and by allowing x to be input as an argument will just open you up to errors and cause confusion. Let's start with this:
myPiecewise[intervals_List] :=
Function[x,
Piecewise[
Table[{x + i, intervals[[i]] <= x < intervals[[i + 1]]},
{i, Length[intervals] - 1}]]]
This will output a function that can just take a value, it doesn't require you to guarantee agreement of formal argument names.
Now let's bundle that into a Plot:
myPiecewisePlot[intervals_List] :=
Plot[myPiecewise[intervals][z],
{z, intervals[[1]], intervals[[-1]]}]
I used z to illustrate that we're no longer dependent on a particular name for the formal argument. Since I've hidden myPiecewise inside myPiecewisePlot, it actually doesn't really matter, but I still like it better. Notice that I'm assuming the plot should start and end with the first and last values of the list provided. That seemed like a reasonable assumption, but I don't know if it's what you want.
Now we're ready for Manipulate:
Manipulate[myPiecewisePlot[list], {{list, {0, 1, 2}}}]
You'll have to be careful to enter your value as a list. You may need to add some validation or coercion to this. Anyway, here's an example where I've changed the interval list.
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Maybe similar with this result.
e = .1;
n = 5;
f[x_, k_] :=
Which @@ Flatten[Table[{i <= x < i + 1 - e, x + i}, {i, k, n}], 1]
Manipulate[
Plot[f[x, k], {x, 1, n}, ExclusionsStyle -> Red,
AxesOrigin -> {0, 0}], {k, 1, n - 1, 1}, ControlPlacement -> Top]
