combining two plots

Question

I have the following two expressions:

v1[z]=(39 z^2)/160 - (23 z^3)/480

and

v2[z]=47/240 - (131 z)/480 + (17 z^3)/480 + z^4/24

I would like to calculate both for z that goes from 0 to 1, but I would like to plot both consecutively, i.e., v1[z] from 0 to 1 and v2[z] from 1 to 2 but evaluated from 0 to 1. How can I do this? Thanks

Answer 1

One way is to join the two functions together into a single Piecewise function:

v1[z_] := (39 z^2)/160 - (23 z^3)/480;
v2[z_] := 47/240 - (131 z)/480 + (17 z^3)/480 + z^4/24;
v[z_] := Piecewise[{{v1[z], 0 <= z <= 1}, {v2[z - 1], 1 <= z <= 2}}]
Plot[v[z], {z, 0, 2}]

Alternatively, you could use UnitBoxes to join the two functions:

v[z_] := v1[z] UnitBox[z - 1/2] + v2[z - 1] UnitBox[z - 3/2];

Answer 2

You can also wrap v1 and v2 with ConditionalExpression:

v1[z_] := (39 z^2)/160 - (23 z^3)/480
v2[z_] := 47/240 - (131 z)/480 + (17 z^3)/480 + z^4/24

Plot[{ConditionalExpression[v1[z], 0 <= z <= 1], 
  ConditionalExpression[v2[z - 1], 1 <= z <= 2]}, {z, 0, 2}, 
 PlotLegends -> "Expressions"]

You can also Translate the primitives of the second plot and combine the two plots using Show:

{plot1, plot2} = Plot[#[z], {z, 0, 1}] & /@ {v1, v2};
Show[plot1, Graphics@Translate[First@plot2, {1, 0}], PlotRange -> All]