dx-doc 1:4.4.4-9 / usr / share / doc / dx / help / dxall955

#!F-adobe-helvetica-medium-r-normal--18*
#!N 
#!N  #!Rstreaml 
Streamline #!N #!N Category #!N #!N  #!Lcatrel,dxall759 h Realization  #!EL  #!N #!N Function #!N 
#!N Computes streamlines to represent the movement of particles through static 
vector fields. #!N #!N Syntax #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N  #!F-adobe-times-bold-r-normal--18*   
line #!EF = Streamline(  #!F-adobe-times-bold-r-normal--18*   data, start, time, head, curl, flag, 
stepscale #!EF ); #!EF #!N #!N #!EC #!N #!N Inputs #!T,1,91,276,461,646 
 #!F-adobe-times-medium-r-normal--14*    #!F-adobe-times-bold-r-normal--18*   #!N TAB Name TAB Type TAB Default TAB Description 
#!EF #!N TAB data TAB vector field TAB none TAB vector 
field #!N TAB start TAB vector list or geometric field TAB 
center of the first series member TAB starting point(s) #!N TAB 
time TAB scalar list TAB series start time(s) TAB starting time(s) 
#!N TAB head TAB integer TAB final series frame number TAB 
series time-step at which the #!N TAB - TAB - TAB 
- TAB streamlines end #!N TAB curl TAB vector field TAB 
no curl TAB vorticity of vector field(s) #!N TAB flag TAB 
flag TAB input dependent TAB 0: curl not used #!N TAB 
- TAB - TAB - TAB 1: curl used to generate 
twist of #!N TAB - TAB - TAB - TAB streamline(s) 
#!N TAB stepscale TAB value TAB 0.1 TAB step length as 
a fraction of the #!N TAB - TAB - TAB - 
TAB size of the connection element #!N TAB - TAB - 
TAB - TAB #!EF #!N #!N Outputs #!T,1,161,321,646  #!F-adobe-times-medium-r-normal--14*    #!F-adobe-times-bold-r-normal--18*   #!N 
TAB Name TAB Type TAB Description #!EF #!N TAB line TAB 
field or group TAB one or more streamlines #!N TAB - 
TAB - TAB #!EF #!N #!N Functional Details #!N #!N This 
module traces the path of a particle through a static vector 
field in discrete steps. The visual form of this trace is 
a streamline, which starts at a specified time and continues until 
the particle it represents exits from the field or reaches a 
region of zero velocity. #!N #!I0 #!N #!N #!I0 #!N  #!F-adobe-times-bold-r-normal--18*   
 #!F-adobe-times-bold-r-normal--18*   data #!EF #!EF #!I50 #!N specifies a vector field. Vector 
fields are limited to  #!F-adobe-times-medium-i-normal--18*   n #!EF -D vectors defined in 
 #!F-adobe-times-medium-i-normal--18*   n #!EF space; for example, 2-D vectors on a 2-D 
sheet or 3-D vectors defined in a 3-D volume. #!N #!I0 
#!N  #!F-adobe-times-bold-r-normal--18*    #!F-adobe-times-bold-r-normal--18*   start #!EF #!EF #!I50 #!N specifies a set 
of positions at which streamlines originate. It can be either a 
list of positions or a geometric field (e.g., the output of 
a Grid module or even an isosurface). #!N #!I0 #!N  #!F-adobe-times-bold-r-normal--18*   
 #!F-adobe-times-bold-r-normal--18*   time #!EF #!EF #!I50 #!N specifies a set of times 
at which streamlines begin to be traced. The units of time 
correspond to the units of the vector field. That is, a 
particle travelling at a unit velocity moves one unit of distance 
in one unit of time. #!N #!N Both  #!F-adobe-times-bold-r-normal--18*   time #!EF 
and  #!F-adobe-times-bold-r-normal--18*   start #!EF can contain single or multiple elements. If 
either parameter contains a single element, that element is associated with 
each element of the other list. If both parameters contain multiple 
elements, they must contain the same number of elements, which are 
then matched in pairs. #!N #!N You can use the time 
parameter to start different streamlines at different times. Note that for 
the static vector fields used by Streamline, a particle at a 
given location will trace the same streamline, regardless of what time 
it is started. #!N #!I0 #!N  #!F-adobe-times-bold-r-normal--18*    #!F-adobe-times-bold-r-normal--18*   head #!EF #!EF 
#!I50 #!N specifies an expiration time for streamlines that have not 
otherwise terminated. The streamline points are computed iteratively, and the spacing 
between the points depends on the element size of the connections 
and the stepscale. If this maximum is reached, a warning is 
produced and the streamline is terminated. The maximum number of streamline 
points is 25,000. #!N #!I0 #!N  #!F-adobe-times-bold-r-normal--18*    #!F-adobe-times-bold-r-normal--18*   curl #!EF #!EF 
#!I50 #!N causes Streamline to produce normals and binormals components that 
represent the vorticity of the vector field.  #!Ldivcurl,dxall827 h DivCurl  #!EL  ). In that 
case, the default value for  #!F-adobe-times-bold-r-normal--18*   flag #!EF is 1. The 
"normals" and "binormals" components of the resulting streamlines rotate according to 
the vorticity of the vector field. This information is either interpolated 
from the vector field passed in as the  #!F-adobe-times-bold-r-normal--18*   curl #!EF 
parameter or is computed internally. #!N #!I0 #!N  #!F-adobe-times-bold-r-normal--18*    #!F-adobe-times-bold-r-normal--18*   flag 
#!EF #!EF #!I50 #!N specifies whether or not the twist specified 
by  #!F-adobe-times-bold-r-normal--18*   curl #!EF is enabled. A setting of 0 (zero) 
disables the twist. #!N #!N However, if  #!F-adobe-times-bold-r-normal--18*   curl #!EF is 
not specified, the default value for  #!F-adobe-times-bold-r-normal--18*   flag #!EF is 0, 
and no twist is produced. In that case you have the 
option of setting  #!F-adobe-times-bold-r-normal--18*   flag #!EF to 1, which causes Streamline 
to compute the curl internally. #!N #!I0 #!N  #!F-adobe-times-bold-r-normal--18*    #!F-adobe-times-bold-r-normal--18*   stepscale 
#!EF #!EF #!I50 #!N specifies the accuracy of the interpolation. Streamline 
traces the path of a particle through the vector field in 
discrete steps. These steps are determined by interpolating a vector from 
the vector field at the current end of the streamline and 
appending a new segment that extends the streamline in the direction 
of the vector. #!N #!N The length of the new segment 
is determined by two factors. First, the length of the projection 
of the segment along the edges of the cells of the 
prior and subsequent vector fields in which the starting point of 
the segment is found does not exceed a proportion (specified by 
the  #!F-adobe-times-bold-r-normal--18*   stepscale #!EF parameter) of the length of the edge. 
Second, if grid is irregular, the segment is truncated at the 
boundary of the element in which it begins. This allows the 
segment length to be determined anew for the next element. #!N 
#!N Thus the  #!F-adobe-times-bold-r-normal--18*   stepscale #!EF parameter offers the user control 
over the accuracy of the streamline. If  #!F-adobe-times-bold-r-normal--18*   stepscale #!EF is 
a small value (perhaps in the range of 0.01 to 0.05), 
the resulting streamline contains a relatively large number of segments that 
closely trace small variations in the vector field. If  #!F-adobe-times-bold-r-normal--18*   stepscale 
#!EF is assigned a large number (0.5 to 1), the steps 
are larger and less accurate, but require less execution time. Note, 
however, that since the step is determined as a proportion of 
the size of the grid cell in which it is contained, 
the segments are small in areas in which the grid elements 
are small, and proportionally larger in areas in which the grid 
elements are large. #!I0 #!N #!N #!N #!N Streamlines trace particles 
through time. Associated with the streamline is a "time" component that 
indicates, for each position of the streamline, the time at which 
the particle reached that position. The initial value in this component, 
therefore, is equal to the starting time for that stream, which 
is by default the first series position, or settable by the 
user using the  #!F-adobe-times-bold-r-normal--18*   time #!EF parameter. The final value in 
the time component is equal to (1) the time at which 
the particle exits from the vector field or (2) the time 
specified by the  #!F-adobe-times-bold-r-normal--18*   head #!EF parameter. #!N #!N The output 
streamlines also contain a "data" component that indicates the velocity of 
the data field at each position in the streamline. #!N #!N 
Components #!N #!N Creates new "positions," "connections," "data," "time," and "colors" 
components. If the flag argument is set, "normals" and "binormals" components 
are also created. #!N #!N Example Visual Programs #!CForestGreen #!N #!N 
 #!F-adobe-courier-bold-r-normal--18*   #!N Interop.net #!N InvalidData.net #!N RubberTube.net #!N Streamline.net #!N ThunderStreamlines.net 
#!EF #!N #!N #!EC #!N #!N See Also #!N #!N  #!Ldivcurl,dxall827 h DivCurl  #!EL  
,  #!Lglyph,dxall856 h Glyph  #!EL  ,  #!Lribbon,dxall927 h Ribbon  #!EL  ,  #!Lstreakl,dxall954 h Streakline  #!EL  ,  #!Ltube,dxall971 h Tube  #!EL  #!N #!N #!N 
 #!F-adobe-times-medium-i-normal--18*   Next Topic #!EF #!N #!N  #!Lstring,dxall956 h String  #!EL  #!N  #!F-adobe-times-medium-i-normal--18*   #!N