Editing Guide to madagascar programs (section)

==sfreverse==
{| class="wikitable" align="center" cellspacing="0" border="1"
! colspan="4" style="background:#ffdead;" | Reverse one or more axes in the data hypercube. 
|-
! colspan="4" | sfreverse < in.rsf > out.rsf which=-1 verb=n memsize=sf_memsize() opt=
|-
| ''int    '' || '''memsize=sf_memsize()''' ||   || 	Max amount of RAM (in Mb) to be used
|-
| ''string '' || '''opt=''' ||   || 	If y, change o and d parameters on the reversed axis;
:if i, don't change o and d
|-
| ''bool   '' || '''verb=n''' ||  [y/n] || 	Verbosity flag
|-
| ''int    '' || '''which=-1''' ||   || 	Which axis to reverse.
:To reverse a given axis, start with 0,
:add 1 to number to reverse n1 dimension,
:add 2 to number to reverse n2 dimension,
:add 4 to number to reverse n3 dimension, etc.
:Thus, which=7 would reverse the first three dimensions,
:which=5 just n1 and n3, etc.
:which=0 will just pass the input on through unchanged.
|}
Here is an example of using <tt>sfreverse</tt>. First, let us create a
2-D dataset.
<pre>
bash$ sfmath n1=5 d1=1 n2=3 d2=1 output=x1+x2 > test.rsf
bash$ < test.rsf sfdisfil
   0:             0            1            2            3            4
   5:             1            2            3            4            5
  10:             2            3            4            5            6
</pre>
Reversing the first axis:
<pre>
bash$ < test.rsf sfreverse which=1 | sfdisfil
   0:             4            3            2            1            0
   5:             5            4            3            2            1
  10:             6            5            4            3            2
</pre>
Reversing the second axis:
<pre>
bash$ < test.rsf sfreverse which=2 | sfdisfil
   0:             2            3            4            5            6
   5:             1            2            3            4            5
  10:             0            1            2            3            4
</pre>
Reversing both the first and the second axis:
<pre>
bash$ < test.rsf sfreverse which=3 | sfdisfil
   0:             2            3            4            5            6
   5:             1            2            3            4            5
  10:             0            1            2            3            4
</pre>
As you can see, the <tt>which=</tt> parameter controls the axes that are
being reversed by encoding them into one number.
When an axis is reversed, what happens with its axis origin and
sampling parameters? This behavior is controlled by <tt>opt=</tt>. In
our example,
<pre>
bash$ < test.rsf sfget n1 o1 d1
n1=5
o1=0
d1=1
bash$ < test.rsf sfreverse which=1 | sfget o1 d1
o1=4
d1=-1
</pre>
The default behavior (equivalent to <tt>opt=y</tt>) puts the origin
<tt>o1</tt> at the end of the axis and reverses the sampling parameter
<tt>d1</tt>.  Using <tt>opt=n</tt> preserves the sampling but reverses
the origin.
<pre>
bash$ < test.rsf sfreverse which=1 opt=n | sfget o1 d1
o1=-4
d1=1
</pre>
Using <tt>opt=i</tt> preserves both the sampling and the origin while
reversing the axis.
<pre>
bash$ < test.rsf sfreverse which=1 opt=i | sfget o1 d1
o1=0
d1=1
</pre>
One of the three possible behaviors may be desirable depending on the
application.