Editing Guide to madagascar programs (section)

==sfmath==
{| class="wikitable" align="center" cellspacing="0" border="1"
! colspan="4" style="background:#ffdead;" | Mathematical operations on data files.
|-
! colspan="4" | sfmath > out.rsf nostdin=n n#= d#=(1,1,...) o#=(0,0,...) label#= unit#= type= label= unit= output=
|-
|  colspan="4" | <br>Known functions: <br>cos,  sin,  tan,  acos,  asin,  atan, <br>cosh, sinh, tanh, acosh, asinh, atanh,<br>exp,  log,  sqrt, abs,<br>erf,  erfc, sign (for float data),<br>arg,  conj, real, imag (for complex data).<br><br>sfmath will work on float or complex data, but all the input and output<br>files must be of the same data type.<br><br>An alternative to sfmath is sfadd, which may be more efficient, but is<br>less versatile.<br><br>Examples:<br><br>sfmath x=file1.rsf y=file2.rsf power=file3.rsf output='sin((x+2*y)^power)' > out.rsf<br>sfmath < file1.rsf tau=file2.rsf output='exp(tau*input)' > out.rsf<br>sfmath n1=100 type=complex output="exp(I*x1)" > out.rsf<br><br>Arguments which are not treated as variables in mathematical expressions:<br>datapath=, type=, out=<br><br>See also: sfheadermath.
|-
| ''float  '' || '''d#=(1,1,...)''' ||   || 	sampling on #-th axis
|-
| ''string '' || '''label=''' ||   || 	data label
|-
| ''string '' || '''label#=''' ||   || 	label on #-th axis
|-
| ''largeint'' || '''n#=''' ||   || 	size of #-th axis
|-
| ''bool   '' || '''nostdin=n''' ||  [y/n] || 	y - ignore stdin
|-
| ''float  '' || '''o#=(0,0,...)''' ||   || 	origin on #-th axis
|-
| ''string '' || '''output=''' ||   || 	Mathematical description of the output
|-
| ''string '' || '''type=''' ||   || 	output data type [float,complex]
|-
| ''string '' || '''unit=''' ||   || 	data unit
|-
| ''string '' || '''unit#=''' ||   || 	unit on #-th axis
|}

<tt>sfmath</tt> is a versatile program for mathematical operations
with RSF files. It can operate with several input files with the
same dimensions and data type. The data type can be real (floating
point) or complex. The following example demonstrates several
features of <tt>sfmath</tt>.
<pre>
bash$ sfmath n1=629 d1=0.01 o1=0 n2=40 d2=1 o2=5 \
output="x2*(8+sin(6*x1+x2/10))" > rad.rsf
bash$ < rad.rsf sfrtoc | sfmath output="input*exp(I*x1)" > rose.rsf
bash$ < rose.rsf sfgraph title=Rose screenratio=1 wantaxis=n | sfpen
</pre>
The first line creates a 2-D dataset that consists of 40 traces 629
samples each. The values of the data are computed with the formula
<font color="#cd4b19">"x2*(8+sin(6*x1+x2/10))"</font>, where <tt>x1</tt> refers to the
coordinate on the first axis, and <tt>x2</tt> is the coordinate of the
second axis. In the second line, we convert the data from real to
complex using <tt>sfrtoc</tt> and produce a complex dataset using
formula <font color="#cd4b19">"input*exp(I*x1)"</font>, where <tt>input</tt> refers to the
input file. Finally, we plot the complex data as a collection of
parametric curves using <tt>sfgraph</tt> and display the result using
<tt>sfpen</tt>.  The plot appearing on your screen should look similar
to the figure.
[[Image:rose.png|frame|center|This figure was created with <tt>sfmath</tt>.]]
One possible alternative to the second line above is
<pre>
bash$ < rad.rsf sfmath output=x1 > ang.rsf
bash$ sfmath r=rad.rsf a=ang.rsf output="r*cos(a)" > cos.rsf
bash$ sfmath r=rad.rsf a=ang.rsf output="r*sin(a)" > sin.rsf
bash$ sfcmplx cos.rsf sin.rsf > rose.rsf
</pre>
Here we refer to input files by names (<tt>r</tt> and <tt>a</tt>) and combine the names in a formula.

Functions can be nested and combined, and variable names, as well as the <tt>input</tt> keyword, may be combined with the axes keywords <tt>x1</tt>, <tt>x2</tt>, etc. Here is an example that shifts a wavelet -0.4s to t=0, computes the frequency-domain complex square root (equivalent to the convolutional square root in time), and shifts the result back to t=0.4s:
<syntaxhighlight lang="bash">
pi=3.14159265
tshift=0.4

sfspike n1=256 k1=101 |\
sfbandpass flo=4 fhi=30 |\
sffft1 opt=n sym=y |\
sfmath output="sqrt(input*exp(2*$pi*$tshift*x1*I))*exp(-2*$pi*$tshift*x1*I)" |\
sffft1 opt=n sym=y inv=y |\
sfgraph |\
sfpen
</syntaxhighlight>