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From: Alan G Isaac <aisaac@am...>  20080717 22:55:34

On Thu, 17 Jul 2008, Dan Reinholz apparently wrote: > title="$\tau$" Use raw strings: http://docs.python.org/tut/node5.html#SECTION005120000000000000000 Cheers, Alan Isaac 
From: Dan Reinholz <xaenn@ya...>  20080717 22:36:57

I'm having a bit of trouble labeling some graphs of mine. The first one is: from pyx import * from pyx.graph import axis g = graph.graphxy(width=8, x=axis.linear(min=1, max=10, title="$\tau$"), y=axis.linear(title="$R(\sqrt{0.5\tau})$")) g.plot(graph.data.function("y(x)= sqrt(0.5*x)/((sqrt(0.5*x) +0.5)*(sqrt(0.5*x)+x))",points=500)) g.finish() g.writeEPSfile("derivatives_opt_1") The problem is that rather than showing the Greek letter tau the output is 5au. My understanding was I could just use LaTeX labels directly, but perhaps I'm doing something wrong? The second is a similar problem. I have another graph: from pyx import * from pyx.graph import axis g = graph.graphxy(width=8, x=axis.linear(min=1, max=10, title="$\tau$"), y=axis.linear(title="$\frac{\sqrt{0.5\tau}}{\sqrt{0.5\tau}+\tau}$")) g.plot(graph.data.function("y(x)=sqrt(0.5*x)/(sqrt(0.5*x)+x)",points=500)) g.finish() g.writeEPSfile("derivatives_opt_2") where here I actually want use a fraction in the label. Trying to do so python becomes very unhappy with me bsd% python derivatives_opt_2.py Traceback (most recent call last): File "derivatives_opt_2.py", line 10, in <module> g.finish() File "/usr/local/lib/python2.5/sitepackages/pyx/graph/graph.py", line 268, in finish self.doaxes() File "/usr/local/lib/python2.5/sitepackages/pyx/graph/graph.py", line 491, in doaxes self.dolayout() File "/usr/local/lib/python2.5/sitepackages/pyx/graph/graph.py", line 475, in dolayout self.doaxiscreate(axisname) File "/usr/local/lib/python2.5/sitepackages/pyx/graph/graph.py", line 216, in doaxiscreate self.axes[axisname].create() File "/usr/local/lib/python2.5/sitepackages/pyx/graph/axis/axis.py", line 565, in create self.canvas = self.axis.create(self.data, self.positioner, self.graphtexrunner, self.errorname) File "/usr/local/lib/python2.5/sitepackages/pyx/graph/axis/axis.py", line 228, in create return _regularaxis._create(self, data, positioner, graphtexrunner, self.parter, self.rater, errorname) File "/usr/local/lib/python2.5/sitepackages/pyx/graph/axis/axis.py", line 198, in _create variants[0].storedcanvas = layout(variants[0]) File "/usr/local/lib/python2.5/sitepackages/pyx/graph/axis/axis.py", line 133, in layout self.painter.paint(canvas, data, self, positioner) File "/usr/local/lib/python2.5/sitepackages/pyx/graph/axis/painter.py", line 253, in paint _title.paint(self, canvas, data, axis, axispos) File "/usr/local/lib/python2.5/sitepackages/pyx/graph/axis/painter.py", line 104, in paint title = canvas.text_pt(x, y, axis.title, titleattrs) File "/usr/local/lib/python2.5/sitepackages/pyx/canvas.py", line 319, in text_pt return self.insert(self.texrunner.text_pt(x, y, atext, *args)) File "/usr/local/lib/python2.5/sitepackages/pyx/text.py", line 1222, in text_pt return self.text(x * unit.t_pt, y * unit.t_pt, expr, *args, **kwargs) File "/usr/local/lib/python2.5/sitepackages/pyx/text.py", line 1201, in text self.finishdvi(ignoretail=1) File "/usr/local/lib/python2.5/sitepackages/pyx/text.py", line 1044, in finishdvi self.execute(None, self.defaulttexmessagesend + self.texmessagesend) File "/usr/local/lib/python2.5/sitepackages/pyx/text.py", line 1036, in execute raise TexResultError("unhandled TeX response (might be an error)", self) pyx.text.TexResultError: unhandled TeX response (might be an error) The expression passed to TeX was: \end% After parsing the return message from TeX, the following was left: *[1] Am I doing something wrong here, or is it just not possible to create labels using fractions? All help is greatly appreciated as always. Thanks, Daniel 
From: Dan Reinholz <xaenn@ya...>  20080717 18:07:53

Hello all, I've been working on writing some PyX code in order to illustrate the different methods of numerical integration. So far I've succeeded in writing code for all of the different Riemann sums, and the trapezoidal rule. For me this just leaves Simpson's rule to work on (which unfortunately is quite a bit more complicated). Here is my work in progress code: from math import * from pyx import * from pyx.graph import axis #Define Variables def f(x): return sin(x) + x x0,y0 = 0,0 # Starting point for Riemann sum intl = 4 # width of total interval nsubintl = 6 # number of subintervals # Code w0 = intl/nsubintl # width of subinterval g = graph.graphxy(width=8, x=axis.linear(min=0, max=intl, title="$x$"), y=axis.linear(title="$\sin(x) + x$")) g.plot(graph.data.function("y(x)=f(x)", context=locals(), points=500)) for i in range(0, nsubintl): def g(x): if x0+i*w0 <= x <= x0+(i+1)*w0: return (f(x0+i*w0) + f(x0+(i+0.5)*w0) + f(x0+(i+1)*w0) )/(2 * w0 * w0) * x * x + (f(x0+(i+1)*w0)  f(x0+i*w0) )/(2 * w0) * x + f(x0+(i+0.5)*w0) g.plot(graph.data.function("y(x)=g(x)", context=locals(), points=500)) else: g.dolayout() g.stroke(g.ygridpath(0), [style.linestyle.dashed,style.linewidth.Thin]) g.stroke(g.xgridpath(0), [style.linestyle.dashed,style.linewidth.Thin]) g.writeEPSfile("trapezoidal_rule") The problem is that when I run it I get the error: bsd% python simpsons_rule.py Traceback (most recent call last): File "simpsons_rule.py", line 27, in <module> g.plot(graph.data.function("y(x)=g(x)", context=locals(), points=500)) AttributeError: 'function' object has no attribute 'plot' Can anybody shed some light on the problem? As long as I'm on the subject, could anybody help me actually figure out how to shade the regions required for Simpson's rule? In each region I will want to connect three straight lines, with a parabola on top, and then fill the total area with a solid color. When I coded the trapezoidal rule, I used: trap = path.path(path.moveto(x1+i*w1,y1), path.lineto(x1+i*w1, b), path.lineto(x1+(i+1)*w1,c), path.lineto(x1+(i+1)*w1,y1), path.closepath()) g.stroke(trap,[deco.filled([color.gray(0.8)]) ]) but I'm not sure how to actually include a curved portion (the parabola) as part of a path. Any suggestions would be greatly appreciated. For reference here is the working code I'm using for the left Riemann sum: from math import * from pyx import * from pyx.graph import axis #Define Variables def f(x): return sin(x) + x x0,y0 = 0,0 # Starting point for Riemann sum intl = 2*pi # width of total interval nsubintl = 20 # number of subintervals # Code g = graph.graphxy(width=8, x=axis.linear(min=0, max=intl, title="$x$"), y=axis.linear(title="$\sin(x) + x$")) g.plot(graph.data.function("y(x)=f(x)", context=locals(), points=500)) g.dolayout() g.stroke(g.ygridpath(0), [style.linestyle.dashed,style.linewidth.Thin]) g.stroke(g.xgridpath(0), [style.linestyle.dashed,style.linewidth.Thin]) # Left Riemann Sum x1,y1 = g.pos(x0,y0) # Starting point on the graph itself x2,y2 = g.pos(x0+intl/nsubintl, 0) # Need to find out the distance of intl/subintl on the graph w0 = intl/nsubintl # width of subinterval w1= x2x1 # width of subinterval on the graph # rect2 = path.rect(a, b, c, d), (a,b) origin, c width, d height. for i in range(0, nsubintl): a,b = g.pos(x0,f(x1+i*w0)) # Get the height of the function b (a is useless) h = b  y1 g.stroke(path.rect(x1+i*w1,y1,w1,h),[deco.filled([color.gray(0.8)]) ]) else: g.writeEPSfile("left_riemann_sum") It's probably not the neatest or best way to achieve my goals, but it works nonetheless. Many thanks, Daniel 