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//genesis - logifier.g - used to plot log(Vm)
/*********************************************************************** \
****
As the GENESIS xgraph object doesn't have a way to plot with a logarithmic
scale, we create a "logifier" object which uses a lookup table to calculate
a natural log. The log of a quantity can then be plotted with messages
like:
sendmsg /cell/soma /logtable INPUT Vm
sendmsg /logtable loggraph PLOT output *soma *black
************************************************************************ \
***/
function make_logtable
int xdivs = 5000
int xmax = 500
int i
float dx
float x
float y
// We may later want to scale and shift the plot
float SCALE = 1.0
// if the range includes x = 0.
float OFFSET = 0.0
create table /logtable
call logtable TABCREATE {xdivs} 0 {xmax}
//call table TABCREATE xdivs xmin xmax (mV)
dx = {getfield logtable table->dx}
// this will be 0.0
x = {getfield logtable table->xmin}
// kludge to set log(0) = log(dx)
y = SCALE*{log {dx + OFFSET}}
setfield logtable table->table[{0}] {y}
x = x + dx
for (i = 1; i <= (xdivs); i = i + 1)
// OFFSET needed if x < 0
y = SCALE*{log {x + OFFSET}}
setfield logtable table->table[{i}] {y}
x = x + dx
end
end
// By default the table uses linear interpolation, which is what we want.
// do it
make_logtable
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