feb 20, 2002soumya mohanty, aei1 geo++ a general purpose c++ dsp library plan of presentation soumya...

Feb 20, 2002 Soumya Mohanty, AEI 1

GEO++A general purpose C++ DSP library

Plan of presentation Soumya Mohanty: Overview R. Balasubramanian: MPI Shell, Frame IO, FFT David Churches: Database IO Stas Babak: PSD: GEO++ Code examples R. Balasubramanian: A simple data monitor using GEO++


GEO++: What is it? Digital Signal Processing (DSP) library in C++

Also included: MPI Shell, Frame reader, Database IO Designed for analysis of a large volume of continuous data

Uses: Implement the DCR algorithm (original motivation) Implement simple data monitors Support Burst and Inspiral searches (mainly IO)

Some facts: About 6000 lines of code written & tested. Started Oct 2001 Under CVS control. Documented using DOC++ 4 programmers working part time (weekly teleconferences + a

visit). Initially 1 experienced in C++ and C, 2 in C, 1 in Java & C


OOPObject Oriented Programming: Some terminology

Consider the implementation of a filter

Input : fixed length sequences state information has to be stored to make the

output sequences continuous Options for a procedural code:

Internal storage inside the function: use static variables several filters cannot be executed using one function

external storage means calling code has to manage what should be a hidden detail

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OOP (II) OOP solution : from function to object A filter object can store state info and implement

a filter function Several objects of filter class can exist

simultaneously each with its own state External code only knows the interface to this

object: setting filter coefficients, setting input and output

Data hiding more reliability for a client code Other important features in OOP: inheritance,

polymorphism


Design Choices (I) DSP consists of mapping one matrix into

another. A lot of DSP is about designing the right map for a given purpose Discrete Fourier Transform maps one vector to another while

preserving size Spectrogram maps a vector to a matrix

GEO++ design reflects this notion: Data container class Matrix Map classes with Matrices as input/output Map Design classes such as filter design


Design Choices (II)GEO++ Data Containers

Essentially one class: Matrix Intuitive to use Actual code: A=B+C; A=B*C; A=0.0; A(5,2)=10.0;

Auxiliary classes : IndexSet, MViewer A(I,J)=10.0; //Multiple rows and columns accessed MViewer object acts as a movable window on a bigger matrix Multiple views can be attached to the same matrix Mixed expressions allowed: C=A+B(I,J);

Matrix class is derived from the C++ Standard Template Library (STL) vector class Advantage: Memory management already taken care of in

STL. we did not write a single line of code for this task.


Design Choices (II)Templates and STL

Example: double and float arrays are usually used in the same way but require duplicate code

Template class: code written with a placeholder for data type

STL: Entirely template based library of fundamental data structures and algorithms. Part of ANSI C++ standard STL Algorithms: sort, find, Set operations etc. can be used on

Matrix. Thus we already have a lot of basic Matlab functions. Other data containers such as linked lists, stacks, Sets etc., exist Disadvantage: cannot make a shared object library. Provision

exists in ANSI C++ standard. Wait for future compiler versions


Design Choices (III)Maps (I)

Maps: Filter, FFTFilt, FastFT, PSD (Welch & AR), Demod, Modulate,

ShiftSamples, RngMedian, Resampling, SortMatrix

STL already has functions which simply need to be wrapped in a class SortMatrix is an example SortMatrix also finds original indices of sorted elements: not

in STL sort

Interface: common names for public members SetInput, SetOutput, SetParameters, Run, Reset Convenient from the user’s point of view


Design Choices (III)Maps (II)

All maps preserve state Meant for analyzing data from interferometers continuously

All maps have default constructors STL vector of maps: elegant way to implement a filter bank

Uniformly named private members AllocInternals, GetState, StoreState, ... Supports code maintenance

To do: Maps should take Map Design objects as arguments FFTFilt could take a type argument that represents different

design methods Create Abstract Base classes to derive sets of maps from


Other GEO++ components Map Design

Window FirWin: Window based FIR filter design Both are template classes FirWin takes Window type as a type argument

Frame IO, Database IO, MPI Shell Following presentations


Summary GEO++ design choices have proven to be elegant

and efficient Great environment for rapid development of C++

DSP codes Future:

Polish Documentation Add Frame writing and database Input functionality More filter design tools and Integrate LAPACK++

GEO++ will soon be open to all interested users and developers

feb 20, 2002soumya mohanty, aei1 geo++ a general purpose c++ dsp library plan of presentation soumya...

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