PtrVector
gather · getval · label · plot · pset · ptr_update_callback · resize · scatter · setval · size

# PtrVector¶

class PtrVector
Syntax:
pv = h.PtrVector(size)

Description:

Fast scatter and gather from a Vector to a list of pointers (must have same length). The size of the pointer vector is fixed at creation and must be an integer greater than 0. Pointers to variables are specified with the pset method. At creation, all pointers point to an internal dummy variable. So it is possible to scatter from a larger Vector into a smaller Vector.

If CVode.cache_efficient() is used, a callback should be registered with the PtrVector.ptr_update_callback() method in order to prevent memory segfaults when internal memory is reallocated.

Example:

from neuron import h
a = h.Vector(5).indgen()
b = h.Vector(5).fill(0)
pv = h.PtrVector(5)
for i in range(len(a)):
pv.pset(i, b._ref_x[i])

pv.scatter(a)
b.printf()
b.mul(10)
pv.gather(a)
a.printf()


PtrVector.size()
Syntax:
length = pv.size()
Description:
Return the number of elements in the PtrVector.

PtrVector.resize()
Syntax:
newsize = pv.resize(newsize)
Description:
Old pointer array is freed and new pointer array with specified size is created. All the pointers point to a dummy variable. If the specified new size is the same as the old size, the old existing array is kept. Newsize must be an integer greater than 0.

PtrVector.pset()
Syntax:
var_val = pv.pset(i, _ref_var)
Description:
The ith pointer in the PtrVector points to var. 0 <= i < pv.size()

PtrVector.scatter()
Syntax:
0. = pv.scatter(srcvec)
Description:
The elements of the Vector argument are copied to the variables pointed to. The size of the Vector must be the same as the size of the PtrVector

PtrVector.gather()
Syntax:
0. = pv.gather(destvec)
Description:
The variable values pointed to by the PtrVector are copied into the destination Vector.

PtrVector.getval()
Syntax:
val = pv.getval(i)
Description:
Return the value pointed to by the ith pointer in the PtrVector.

PtrVector.setval()
Syntax:
val = pv.getval(i, x)
Description:
Set the variable pointed to by the ith pointer to the value of x.

PtrVector.ptr_update_callback()
Syntax:

pv.ptr_update_callback(pythoncallback)

pv.ptr_update_callback("hoc_statement", [object])

Description:
The statement or pythoncallback is executed whenever range variables are re-allocated in order to establish cache efficiency. (see CVode.cache_efficient()) Within the callback, the PtrVector.resize() method may be called but the PtrVector should not be destroyed. The return value is 0.

PtrVector.plot()
Syntax:

0 = pv.plot(graphobj)

0 = pv.plot(graphobj, color, brush)

0 = pv.plot(graphobj, x_vec)

0 = pv.plot(graphobj, x_vec, color, brush)

0 = pv.plot(graphobj, x_increment)

0 = pv.plot(graphobj, x_increment, color, brush)

Description:

Analogous to Vector.plot() but always returns 0 instead of self. Plots the pointer vector elements in a Graph object. The default is to plot the dereferenced elements of the pointer vector as y values with their indices as x values. An optional argument can be used to specify the x-axis. Such an argument can be either a vector, x_vec, in which case its values are used for x values, or a scalar, x_increment, in which case x is incremented according to this number.

This function plots the pv.getval(i) values that are pointed to by the pointer vector at the time of graph flushing or window resizing. There is currently no corresponding alternative to Vector.line() which plots the vector values that exist at the time of the call to plot. So the best way to produce multiple line plots is to first PtrVector.gather() into a Vector and use vec.line().

Once a pointer vector is plotted, it is only necessary to call graphobj.flush() in order to display further changes to the valuses pointed to. In this way it is possible to produce rather rapid line animation.

If the vector PtrVector.label() is not empty it will be used as the label for the line on the Graph.

Resizing a pointer vector that has been plotted will remove it from the Graph.

The number of points plotted is the minimum of vec.size and x_vec.size at the time pv.plot is called. x_vec is assumed to be an unchanging Vector.

Example:

from neuron import h, gui
import time

g = h.Graph()
g.size(0,10,-1,1)
vec = h.Vector()
vec.indgen(0,10, .1)
vec.apply("sin")

pv = h.PtrVector(len(vec))
pv.label("PtrVector")
for i in range(len(vec)):
pv.pset(i, vec._ref_x[i])

pv.plot(g, .1)
def do_run():
for i in range(len(vec)):
vec.rotate(1)
g.flush()
h.doNotify()
time.sleep(0.01)

h.xpanel("")
h.xbutton("run", do_run)
h.xpanel()


PtrVector.label()
Syntax:

curstr = pv.label("str")

curstr = pv.label()

Description:
Set the label to the string arg. Return the current label. When plotting, the label will be displayed. Very similar to functionality of Vector.label().