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fixed gouraud error in pcolormesh #26320

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fixed gouraud error in pcolormesh #26320

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10 changes: 7 additions & 3 deletions lib/matplotlib/axes/_axes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5820,9 +5820,13 @@ def _pcolorargs(self, funcname, *args, shading='auto', **kwargs):
f" see help({funcname})")
else: # ['nearest', 'gouraud']:
if (Nx, Ny) != (ncols, nrows):
raise TypeError('Dimensions of C %s are incompatible with'
' X (%d) and/or Y (%d); see help(%s)' % (
C.shape, Nx, Ny, funcname))
if (Nx, Ny) == (ncols + 1, nrows + 1):
X = (X[1:, 1:] + X[:1, :-1]) / 2
Y = (Y[1:, :-1] + Y[:-1, :-1]) / 2
Comment on lines +5824 to +5825
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I haven't looked at these shapes in detail, but shouldn't these be consistent?

Suggested change
X = (X[1:, 1:] + X[:1, :-1]) / 2
Y = (Y[1:, :-1] + Y[:-1, :-1]) / 2
X = (X[1:, 1:] + X[:-1, :-1]) / 2
Y = (Y[1:, 1:] + Y[:-1, :-1]) / 2

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Might work, but I thought is made more since to change the X and Y boundary points independently.

else:
raise TypeError('Dimensions of C %s are incompatible with'
' X (%d) and/or Y (%d); see help(%s)' % (
C.shape, Nx, Ny, funcname))
if shading == 'nearest':
# grid is specified at the center, so define corners
# at the midpoints between the grid centers and then use the
Expand Down
21 changes: 19 additions & 2 deletions lib/matplotlib/tests/test_axes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1399,6 +1399,19 @@ def test_pcolormesh_alpha():
ax4.pcolormesh(Qx, Qy, Z, cmap=cmap, shading='gouraud', zorder=1)


@check_figures_equal()
def test_pcolormesh_gouraud(fig_test, fig_ref):
ax_test = fig_test.subplots()
ax_ref = fig_ref.subplots()
x = np.arange(-4, 5)
y = np.arange(-6, 7)
xe = np.linspace(-4.5, 4.5, 10)
ye = np.linspace(-6.5, 6.5, 14)
c = np.exp(-0.5*0.125*(x.reshape(1, -1)**2 + y.reshape(-1, 1)**2))
ax_ref.pcolormesh(x, y, c, shading='gouraud')
ax_test.pcolormesh(xe, ye, c, shading='gouraud')


@pytest.mark.parametrize("dims,alpha", [(3, 1), (4, 0.5)])
@check_figures_equal(extensions=["png"])
def test_pcolormesh_rgba(fig_test, fig_ref, dims, alpha):
Expand Down Expand Up @@ -1476,9 +1489,13 @@ def test_pcolorargs():
with pytest.raises(TypeError):
ax.pcolormesh(X, Y, Z.T)
with pytest.raises(TypeError):
ax.pcolormesh(x, y, Z[:-1, :-1], shading="gouraud")
ax.pcolormesh(x, y, Z[:-2, :-2], shading="gouraud")
with pytest.raises(TypeError):
ax.pcolormesh(X, Y, Z[:-2, :-2], shading="gouraud")
with pytest.raises(TypeError):
ax.pcolormesh(x[1:], y[1:], Z, shading="gouraud")
with pytest.raises(TypeError):
ax.pcolormesh(X, Y, Z[:-1, :-1], shading="gouraud")
ax.pcolormesh(X[1:, 1:], Y[1:, 1:], Z, shading="gouraud")
x[0] = np.NaN
with pytest.raises(ValueError):
ax.pcolormesh(x, y, Z[:-1, :-1])
Expand Down