Mo-trunk の inkscape-0.46 の関数プロットにあるバグ。inkscape の trunk では修正されていますが、
inkscapeの次のリリースは未だ先だと思うので…

# diff -u /usr/share/inkscape/extensions/funcplot.py.orig /usr/share/inkscape/extensions/funcplot.py
--- /usr/share/inkscape/extensions/funcplot.py.orig 2008-06-27 02:07:22.000000000 +0900
+++ /usr/share/inkscape/extensions/funcplot.py 2008-06-27 02:07:58.000000000 +0900
@@ -114,7 +114,7 @@
dx0 = (x1 - x0)/ds
dy0 = (y1 - y0)/ds
else: # derivative given by the user
- dx0 = 0 # Only works for rectangular coordinates
+ dx0 = 1 # Only works for rectangular coordinates
dy0 = fp(xstart)

# Start curve
@@ -138,7 +138,7 @@
dx1 = (x1 - x2)/ds
dy1 = (y1 - y2)/ds
else: # derivative given by the user
- dx1 = 0 # Only works for rectangular coordinates
+ dx1 = 1 # Only works for rectangular coordinates
dy1 = fp(x1)
# create curve
a.append([' C ',