You can get more information on the expr object at http://www.crca.ucsd.edu/~yadegari/expr.html
New if Version 0.4
-access to variables (made by value object)
-multiple expression separated by ;
-added the following shorthands:
$y or $y1 = $y1[-1] and $y2 = $y2[-1] -new functions:
if - conditional evaluation
cbrt - cube root
erf - error function
erfc - complementary error function
expm1 - exponential minus 1,
log1p - logarithm of 1 plus
isinf - is the value infinite,
finite - is the value finite
isnan -- is the resut a nan (Not a number)
copysign - copy sign of a number
ldexp - multiply floating-point number by integral power of 2
imodf - get signed integral value from floating-point number
modf - get signed fractional value from floating-point number
drem - floating-point remainder function
Thanks to Orm Finnendahl for adding the following functions:
fmod - floating-point remainder function
ceil - ceiling function: smallest integral value not less than argument
floor - largest integral value not greater than argument
New in Version 0.3
-Full function functionality
The object "expr" is used for expression evaluaion of control data.
Expr~ and fexpr~ are extentions to the expr object to work with vectors. The expr~ object is designed to efficiently combine signal and control stream processing by vector operations on the basis of the block size of the environment.
fexpr~ object provides a flexible mechanism for building FIR and IIR filters by evaluating expressions on a sample by sample basis and providing access to prior samples of the input and output audio streams. When fractional offset is used, fexpr~ uses linear interpolation to determine the value of the indexed sample. fexpr~ evaluates the expression for every single sample and at every evaluation previous samples (limited by the audio vector size) can be accessed. $x is used to denote a singnal input whose samples we would like to access. The syntax is $x followed by the inlet number and indexed by brackets, for example $x1[-1] specifies the previous sample of the first inlet. Therefore, if we are to build a simple filter which replaces every sample by the average of that sample and its previous one, we would use "fexpr~ ($x1[0]+$x1[-1])/2 ". For ease of when the brackets are omitted, the current sample is implied, so we can right the previous filter expression as follows: " fexpr~ ($x1+$x1[-1])/2". To build IIR filters $y is used to access the previous samples of the output stream.
The three objects expr, expr~, and fexpr~ are implemented in the same object so the files expr~.pd_linux and fexpr~.pd_linux are links to expr.pd_linux This release has been compiled and tested on Linux 6.0.
Here are some syntax information: (refer to help-expr.pd for examples)
- Syntyax
- The syntax is very close to how expression are written in C. Variables are specified as follows where the '' stands for the inlet number: $i: integer input variable $f: float input variable $s: symbol input variable
Used for expr~ only:
$v#: signal (vector) input (vector by vector evaluation)
Used for fexpr~ only:
$x#[n]: the sample from inlet indexed by n, where n has to
satisfy 0 => n >= -vector size,
($x is a shorthand for $x#[0], specifying the current sample)
$y#[n]: the output value indexed by n, where n has to
satisfy 0 > n >= -vector size,
$y[n] is a shorthand for $y1[n]
I'll appreciate hearing about bugs, comments, suggestions, ...
Shahrokh Yadegari (sdy@ucsd.edu)
7/10/02