Post-Processing Output with MATLAB

Claudia Fricke

Institute of Petroleum Engineering, Heriot Watt University

Overview

• How to create MATLAB Output with CSMP?

• How to use the CSMP Output with MATLAB?

Why MATLAB – not VTK?

Advantages Disadvantages• easy to manipulate data• analyse and compare data from

various calculations by subsequent editing

• automated batch processing• export data in high quality• lots and lots of plot options• possibility to call MATLAB from

C code – lots of other interfaces

• LOTS of possibilities

• sometimes extensive preparations

• so far 3D not implemented in CSMP!

General CSMP++ Workflow

1. Load libraries

2. Generate SuperGroup (from mesh) and set properties, boundary and start values

3. Set up FE and FV algorithms

4. Output initial values

5. Main calculation loop over different time steps

6. Final outputCSMP or MATLAB Code: essential commands in red or green

Include Header-File

1. Load libraries#include "CSP_MatlabInterface.h" *)

2. Generate supergroup (from mesh) and set properties, boundary and start values

3. …

*) in ...\CSMP\source_code\interfaces

CSP_MatlabInterface.h

void write2DMatlabFile(SuperGroup<csp_float,2>& sg, const char* name,const char* variable,long step );

void write2DMatlabFile(SuperGroup<csp_float,2>& sg,const char* groupname,const char* name,const char* variable,long step );

void extractAndWrite1DVariableProfileAlongX( ... );void extractAndWrite1DVariableProfileAlongY( ... );

void writeSavedTimeStepsFile( long step, const char* name="saved_time_steps.txt" );

name of supergroupname of output filesCSMP output variablevalue of CSMP variable to file

save current time step in file

extract 1D data from 2D

current time step

restriction to sub-groupcurrent time stepdefault output filename

Export Initial Values…

3. Set up FE and FV algorithms

4. Output initial valueswrite2DMatlabFile (

supergroup, name of output file,CSMP variable,time step := start time )

writeSavedTimeStepsFile (time step := start time ,"filename" );

5. Main calculation loop over different time steps

…

Export Values for each Time Step

…

5. Main calculation loop over different time stepswhile ( global_time < max_time ) {

...//calculate time step FE / time step FV...write2DMatlabFile(

supergroup, name of output file, CSMP variable,time step := current time )

writeSavedTimeStepsFile( ... );

//increment global_time ... }

…

Export Final Values

...

5. Main calculation loop over different time steps

6. Final outputwrite2DMatlabFile(

supergroup, name of output file,CSMP variable,time step := final time )

writeSavedTimeStepsFile( ... );

Example

CSMP

Finite Element Mesh

m Finite Elements(here m = 8)1

2

6

5

3

4

7

8

n Nodes(here n = 9)

12

6

5

3

4

78

9

Generated Output Files

1

12

3

1

x-y-coordinatesof nodes

one value for each nodeone file for each time step

time steps in extra file

m rows n rows n rows

t files

t rows

Part 2

And now?

How to use the CSMP Output with MATLAB?

How to read data into MATLAB?

variable = load (file name)• returns matrix variable • each matrix column represents a column from the former data table• each matrix row represents one row from the former data table

Command load

n x 2 matrix

variable (:,1)returns 1st column of matrix

n rowsm rows m x 3 matrix

How to plot in 1D?

1D Command plot( nodes on x axis,calculated y-values,plot options)

Plot Options:• multiple plots• plot title• legend• axes markings• change colours• add coordinates grid• size of text• ...

How to plot in 2D?

2D Commands

surface plot (for triangular data)

trisurf(mx3 matrix of triangular

elements,n x-values of nodes,n y-values of nodes,calculated z-values,options)

Mesh Plot trimesh ( matrix of triangular elements,x coordinates of nodes,y coordinates of nodes,options)

one plot command per time step for animation

How to save plot as image file?

print( resolution, file type, file name );

Stack of Images Animation (e.g with Movie Maker)

compose file name (loop counter j)

['concentration', num2str(j),'.jpg']

Command print

Exampleprint( '-r200',

'-djpeg', 'concentration.jpg' );

2D Animation Example% start valuestime_steps = load ('time_steps.txt'); % 1 columnj = 1; %loop counterlast_time_step = length(time_steps);

% load meshno = load ( 'nodes.txt' );el = load ( 'elements.txt' );

% loopwhile j <= last_time_step

u = load ( ['concentration', num2str(j),'.txt'] );trisurf ( el, no(:,1), no(:,2), u, possible options)view ( 2 ) % top view... % more plot options

% save single jpg'sprint( '-r200', '-djpeg', ['concentration', num2str(j),'.jpg'] );

j = j + 1 ; % time step incrementend

% see a plot of just the triangles withtrimesh ( t, no(:,1), no(:,2) )

% start valuestime_steps = load ('time_steps.txt'); % 1 columnj = 1; %loop counterlast_time_step = length(time_steps);% load meshno = load ( 'nodes.txt' );el = load ( 'elements.txt' );

% loopwhile j <= last_time_step

u = load ( ['concentration', num2str(j),'.txt'] );trisurf ( el, no(:,1), no(:,2), u, possible options)view ( 2 ) % top view... % more plot options

% save single jpg'sprint( '-r200', '-djpeg', ['concentration', num2str(j),'.jpg'] );

j = j + 1 ; % time step incrementend% see a plot of just the triangles withtrimesh ( t, no(:,1), no(:,2) )

Output

MATLAB

Change Plot Options withBatch Function

1. Create basic plot

2. Change various plot options with Property Editor

3. Generate m-Code Function

4. Call this function and pass in new datafrom other m-File in main loop

• in detail see Youtube video“MATLAB Plot: Interactively Creating Plots in MATLAB”

http://www.youtube.com/watch?v=GJVvBqR8Mws

Useful Links to MATLAB

Always try Help Manual of MATLAB = easy

MATLAB “homepage”http://www.mathworks.com

…/products/featured/videos/…/academia/student_center/tutorials/launchpad.htmlIntroduction, Tutorials, Documentation, Examples, etc.

Some useful tutorialshttp://www.youtube.com/user/MATLAB

Octave (free alternative, mostly compatible with MATLAB) http://www.octave.org/

1D Output

Extract data from 2D

void extractAndWrite1DVariableProfileAlongY(... );

void extractAndWrite1DVariableProfileAlongX( SuperGroup<csp_float,2>& sg, csp_float distance, const char* name, const char* variable,long step );

1D Post-Processing Plot

• 1-dimensional advection & diffusion equation

• compare different time stepping schemes

• plot 4 results in one figure with MATLAB

extractAndWrite1DVariableProfileAlongX(..)

1D Animation Example% start valuesobs_function = 'fluid_pressure';time_steps = load ('time_steps.txt'); % 1 columnstep = time_steps(2) - time_steps(1);max_time = time_steps(length(time_steps));t = time_steps(1);

while t <= max_time % read CSMP data u = load ( [obs_function, num2str(t),'.txt'] ); %2 columns x = u(:,1); % 1st column p_x_t_CSMP = u(:,2); % 2nd column % calculate analytical solution p_x_t_ana = ...

%plot figure(1) plot( x, p_x_t_ana, x, p_x_t_CSMP)

... % more plot options

t = t + step;end

MATLAB Terms

• Environment:– Command Window– Workspace– Current Directory– Command History

• Programming– m-code– m-file– script vs. function– plot, figure, surface plot, ...