The houdini help said “Returns the value of the second or third argument depending on the truth of the first argument.”.

so, this function's structure is ‘if(expression, true_value, false_value)’

but default value of angular velocity of motion dop parameter has arguments more than 3.

if($DATACT == $ST, 0, angvel(vector3($rx, $ry, $rz), vector3(ch(“rx”), ch(“ry”), ch(“rz”)), $TIMESTEP))

i cant understand this structure.

sorry i cant write english well.

you can imagine it like this

if(

then first argument:

$DATACT == $ST,

second argument:

0,

third argument(everything in angvel() expression):

angvel(
vector3($rx, $ry, $rz),
vector3( ch(“rx”), ch(“ry”), ch(“rz”) ),
$TIMESTEP
)

the end of if
)

tamte
you can imagine it like this

if(

then first argument:

$DATACT == $ST,

second argument:

0,

third argument(everything in angvel() expression):

angvel(
vector3($rx, $ry, $rz),
vector3( ch(“rx”), ch(“ry”), ch(“rz”) ),
$TIMESTEP
)

the end of if
)

thanks for your help!