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<H1><A NAME="SECTION0015300000000000000000"></A>
<A NAME="24170"></A>
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7.30 Trigonometric functions plotted in graph mode
</H1>
<P>
Finally, we end with a simple mathematical illustration of sine and cosine, highlighting the
it graph mode for linear projections and the new curved vectors for angles.
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<PRE>#!/bin/sh
# GMT EXAMPLE 30
#
# Purpose: Show graph mode and math angles
# GMT progs: gmtmath, psbasemap, pstext and psxy
# Unix progs: echo, rm
#
# Draw generic x-y axes with arrows
ps=example_30.ps
psbasemap -R0/360/-1.25/1.75 -JX8i/6i -B90f30:,-\\312:/1g10:."Two Trigonometric Functions":WS -K \
-U"Example 30 in Cookbook" --BASEMAP_TYPE=graph --VECTOR_SHAPE=0.5 > $ps
# Draw sine an cosine curves
gmtmath -T0/360/0.1 T COSD = | psxy -R -J -O -K -W2p >> $ps
gmtmath -T0/360/0.1 T SIND = | psxy -R -J -O -K -W2p,. --PS_LINE_CAP=round >> $ps
# Indicate the x-angle = 120 degrees
psxy -R -J -O -K -W0.5p,- << EOF >> $ps
120 -1.25
120 1.25
EOF
pstext -R -J -O -K -Dj0.05i -N << EOF >> $ps
360 1 18 0 4 RB x = cos(@%12%a@%%)
360 0 18 0 4 RB y = sin(@%12%a@%%)
120 -1.25 14 0 4 LB 120\\312
370 -1.35 24 0 12 LT a
-5 1.85 24 0 4 RT x,y
EOF
# Draw a circle and indicate the 0-70 degree angle
echo 0 0 | psxy -R-1/1/-1/1 -Jx1.5i -O -K -X3.625i -Y2.75i -Sc2i -W1p -N >> $ps
psxy -R -J -O -K -m -W1p << EOF >> $ps
> x-gridline -W0.25p
-1 0
1 0
> y-gridline -W0.25p
0 -1
0 1
> angle = 0
0 0
1 0
> angle = 120
0 0
-0.5 0.866025
> x-projection -W2p
-0.3333 0
0 0
> y-projection -W2p
-0.3333 0.57735
-0.3333 0
EOF
pstext -R -J -O -K -Dj0.05i << EOF >> $ps
-0.16666 0 12 0 4 CT x
-0.3333 0.2888675 12 0 4 RM y
0.22 0.27 12 -30 12 CB a
-0.33333 0.6 12 30 4 LB 120\\312
EOF
echo 0 0 0 120 | psxy -R -J -O -Sml1i -W1p >> $ps
rm -f .gmt*
</PRE>
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<P>
The script simply draws a graph basemap, computes sine and cosine and plots them as lines, then
indicates on a circle that these quantities are simply the projections of an unit vector on the
x- and y-axis, at the given angle.
<P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_example_30"></A><A NAME="25155"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 7.30:</STRONG>
Trigonometric functions plotted in graph mode.</CAPTION>
<TR><TD>
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WIDTH="528" HEIGHT="401" ALIGN="BOTTOM" BORDER="0"
SRC="img208.png"
ALT="\includegraphics[scale=0.5]{scripts/example_30}"></DIV></TD></TR>
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<ADDRESS>
Paul Wessel
2010-01-14
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