Plotting

plot prints a structured record, and the page draws the chart from it. Run a cell to see its output beside the expected one.

plot emits a structured record

figure declares the chart (title, x label, y label) and plot adds a series. Both print records on stdout; the page draws the chart from them and adds nothing of its own.

Viv [1]

x = linspace(0.0, 3.0, 7)
y = zeros(7)
for i to 7 {
    y[i] = x[i] * x[i]
}
figure("A parabola", "x", "x squared")
plot(x, y, "x squared")

A matrix as a heatmap with plot2d

plot2d(Z) or plot2d(Z, "label") renders a rank-2 array as a color map (viridis) with a colorbar. The format of the printed record is fixed, and this example's test fails if it changes.

Viv [2]

Z = zeros(2, 3)
for i to 2 {
    for j to 3 {
        Z[i, j] = i * 3.0 + j
    }
}
figure("A 2 x 3 field", "column", "row")
plot2d(Z, "a tiny field")

A curve in three dimensions with plot3d

plot3d(x, y, z, "label") draws a rotatable 3-D curve — drag the rendered figure to spin it. Three equal-length rank-1 arrays.

Viv [3]

n = 3
xs = linspace(0.0, 1.0, n)
ys = zeros(n)
zs = zeros(n)
for i to n {
    ys[i] = xs[i] * xs[i]
    zs[i] = 1.0 - xs[i]
}
figure("An arc in space", "x", "y")
plot3d(xs, ys, zs, "a short arc")

A histogram

histogram counts into equal bins; bars draws the counts at the bin centers. A plot on the same x afterwards draws a curve over the bars, which is how a measured distribution is shown against a theoretical one.

Viv [4]

v = [0.1, 0.4, 0.45, 0.8, 0.9, 0.95, 1.7, 2.2]
h = histogram(v, 0.0, 2.0, 4)
c = linspace(0.25, 1.75, 4)
figure("Counts per bin", "value", "count")
bars(c, h, "counts")
plot(c, 4.0 - 2.0 * c, "a line over them")

Same x merges into one chart

Consecutive plots sharing an x-array become labeled series on one figure.

Viv [5]

n = 41
x = linspace(0.0, 6.28, n)
s1 = zeros(n)
s2 = zeros(n)
for i to n {
    s1[i] = sin(x[i])
    s2[i] = cos(x[i])
}
figure("Sine and cosine", "x", "value")
plot(x, s1, "sin")
plot(x, s2, "cos")

Different x means different charts

Each chart gets its own figure.

Viv [6]

a_x = linspace(0.0, 1.0, 5)
b_x = linspace(0.0, 2.0, 9)
a_y = zeros(5)
b_y = zeros(9)
for i to 5 { a_y[i] = a_x[i] }
for i to 9 { b_y[i] = b_x[i] * b_x[i] }
figure("A line", "x", "y")
plot(a_x, a_y, "line")
figure("A parabola", "x", "y")
plot(b_x, b_y, "parabola")

figure is required

A chart's title and axis labels are part of the program. Nothing outside it can add them, so a plot with no figure declared does not compile — in any engine.

Viv [7]

x = linspace(0.0, 1.0, 5)
plot(x, x, "a line")

expected error: needs a `figure(title, xlabel, ylabel)` before it…

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