data plotting with matlab - unibs.it · 1. why matlab? why matlab? matlab is a high-level...

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Giulia Valerio 7Marzo 2014 1

DATA PLOTTING WITH MATLAB

Prof. Marco Pilotti [email protected]

Dr. Giulia Valerio

[email protected]

mailto:[email protected]

mailto:[email protected]

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1. WHY MATLAB?

WHY MATLAB?

Matlab is a high-level programming language that provides a numerical computing environment for algorithms development, data visualization and data analysis

The use of Matlab is more appropriate in the following cases:

If you have to evaluate large amounts of data that are acquired automatically by means of computers and other technical appliances.

If you want to develop general programmed data evaluation routines to be applied to different set of data. The application of these routines is a more efficient way if the evaluation procedure has to be changed over and over again to 'fine-tune' it. Re-calculating the whole data set with the changed procedure is then done in a snap.

If you need graphics functions and dedicated statistics functions as well as other interesting features which are not available in other software packages.

Giulia Valerio 5Marzo 2013

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1. WHY MATLAB?

At the end of this lesson you will be able to… http://www.mathworks.it/academia/student_center/tutorials/ps_solve/player.html


http://www.mathworks.it/academia/student_center/tutorials/ps_solve/player.html

http://www.mathworks.it/academia/student_center/tutorials/ps_solve/player.html

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2. MATLAB ENVIRONMENT

MATLAB ENVIRONMENT

1. The «Command Window» area is the communication channel between the user and the Matlab program. Here, commands can be entered,

and programs can output results and messages. Warnings, error messages and the like are also shown here. In the Command Window, previously entered commands can be repeated with the keys <arrow

up> and <arrow down>, and then changed and re-executed.

3. The «Current Directory» browser is used to access the computer's file system. There, you can select the current directory for data

storage as well as the root directory for the editor.

4. The «Workspace» is the working memory of Matlab. It stores the used variables on which programs operate..

2. In the window «Command History» you find the commands you have entered throughout the current session in the

command window.

5. Matlab's help system is an indispensable aid for beginners as well

as experienced users. It makes a printed manual unnecessary. Here you

can also find DEMOS, the on-line tutorials. Otherwise, see

www.mathworks.com

THE USER INTERFACE


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3. MATLAB FUNDAMENTALS

COMMANDS

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SINGLE COMMANDS in the Command window

GROUPS OF COMMANDS in the Matlab editor

SCRIPTS

Notes: % …. to make comments a = 3; without ; shows the variables in the Command window; without doesn’t

You have to type any valid command in the Matlab editor and then save the script as Namefile.m. Back in the Command window, typing Matlab will execute all the commands written in Nomefile.m

Namefile


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4. DATA MANIPULATION

6 Giulia Valerio 5Marzo 2013

Today we will plot some of the data measured by the monitoring station active on Lake Iseo, showing some peculiar aspect of the thermal and

hydrodynamic behaviour of this water body

PRACTICE

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READING AND DEFINING VARIABLES

rv1(2) read the second element of the vector

m1(2, 3) read the element of the matrix m1 in the 2nd row and 3th column

m1(end, 3:4) read the element of the matrix m1 in the last row, 3th and 4th column

EXTRACT SINGLE

ELEMENTS

m2 = m1(2, 3) read back the element of the matrix in the 2nd row and 3th column and assign it to a new variable m2

EXTRACTSINGLE ELEMENTS

AND CREATE NEW VAR


FUNCTION datenum

datenum([aaaa mm dd hh mi ss]) converts a date to a single number [days] that matlab uses to manage time series of data. aaaa is the year, mm is the month, dd is the day, hh is the hour, mi is the minute and ss is the second

A variable is MATRIX, with elements identified by their position

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READING AND DEFINING VARIABLES

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IMPORTING DATA

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A. Import through the IMPORT WIZAD

A1. In the “Current folder” go to the directory of interest

A2. Select the file and right click on “Import”

A3. Specify the “Import parameters”

A4. You will se the data in the “Workspace”

B. Import PROGRAMMATICALLY

B1. cd ‘Nomepath’

B2. new_var = importdata(‘Nomefile.txt’)

new_var = importdata(filename, delimiter, nheaderlines);

B3. You will se the new_var in the “Workspace”

Editing >> doc fileformats you will see the help page where to find more about the supported filetypes and how to extract them



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A. Saving MANUALLY from the workspace

A1. Select with the CNTR-key

A2. Right-click on one of the variable and select Save as

A3. Specify the folder and the Nomefile.mat

B. Saving PROGRAMMATICALLY

Save(filename) stores all variables from the current workspace in a MATLAB formatted binary file (MAT-file) called filename

save(filename, variables) stores only the specified variables.

Matlab FIGURES can be saved into .fig files

or exported as .tif .jpg … file

see Figure – File- Export set up



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SAVING AND LOADING DATA

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Matlab DATA can be easily stored into formatted binary.mat files



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PRACTICE

We want to analyze the hydrodynamic conditions that were observed between 01 and 10 August 2011 in Lake Iseo. Load the data by by following the instructions in the “data.m” script. • Select the directory where you saved the files •Import the temperature.txt file and meteo.txt with the data set measured by the floating station . Meteo.txt includes air temperature, wind and radiation data as a function of time. Temperature.txt include the water temperature data measured at 21 depths as a function of time • Extract the series of time , windspeed, winddirection, temperature and depth in variables called wspeed, wdir, temp and depth. •Keep on the workspace only these last variables and save them as a Iseo.mat file

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4. DATA PLOTTING

MATLAB FOR DATA PLOTTING VISUALIZING DATA - OVERVIEW

http://www.mathworks.it/help/techdoc/creating_plots/f9-53405.html

2D P

LOTTING F

UNCTIONS





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3D P

LOTTING F

UNCTIONS


4. DATA PLOTTING




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VISUALIZING DATA – FIGURE PROPERTIES

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figure create a figure window

clf clear the contents of a figure window

close, close all close figure(s)

hold on, hold off fixate graph, or release fixation

subplot create or address sub-figures

set(gcf, 'property', parameter);

gcf = get current figure handle

Change the properties of a figure window by means of argument pairs, such as: Name, Color, Position, Toolbar, Visible


4. DATA PLOTTING

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plot(X1,Y1,...,Xn,Yn)

If one of Yn or Xn is a matrix and the other is a vector, it plots the vector versus the matrix row or column with a matching dimension to the vector. If Xn is a scalar and Yn is a vector, it plots discrete Yn points vertically at Xn. If Xn or Yn are matrices, they must be 2-D and the same size, and the columns of Yn are plotted against the columns of Xn.

plots each vector Yn versus vector Xn on the same axes.

plot(...,'PropertyName',PropertyValue,...) manipulates plot characteristics

You can find all the properties at: http://www.mathworks.it/help/techdoc/ref/lineseriesproperties.html Among them, the following are particularly useful:

LineStyle: the style of the line (standard, dotted, dashed etc.)

LineWidth : the width of the line

Marker: the style of the data point markers (dot, circle, triangle, star…)

Color : the color of the curve


4. DATA PLOTTING

http://www.mathworks.it/help/techdoc/ref/lineseriesproperties.html

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Example: plot(X1,Y1,’LineStyle’,’-’,’Color’,'b','Linewidth',2)

= plot(X1,Y1,’-b’,'Linewidth',2)


4. DATA PLOTTING

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set(gca, 'property', parameter); gca = get current axeshandle

Change the properties of an axes (see http://www.mathworks.it/help/techdoc/ref/axes_props.html ) Among them, the following are particularly useful:

FontName, FontSize, XLim, Ylim, Xlabel, Ylabel, Xtick, Ytick

xlabel, ylabel, zlabel label an axis

datetick label the axis with a data format (e.g. 01 Jul 2011)

grid on, grid off show or hide the grid

axis on, axis off show or hide the axes

axis([xmin xmax ymin ymax]) set axis limits

axis equal impose the same scale for the axis

Example:

set(gca, 'Xtick',0:0.5:8,'Ytick',0:0.5:6,'FontName',’Arial','FontSize',10);


4. DATA PLOTTING

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PRACTICE

Create a figure (Figure1) that shows the temperature profile T(z) measured the beginning and at the end of the period of interest,

by following the instructions in the “profile.m” script. Use two different colors and a solid line with circles. The vertical axis must be limited between 0 and -50m and spaced every 5m and

must have “z (m)” as label. The vertical axis must be limited between 5 and 30m and spaced every 5°C and must have “T (°C)”

as label. Use Arial 10 as font. Add the lagend. Once the figure has been created, modify the dimension of the

plot, fix the resolution of the figure as 300 dpi. Save the figures both as Profile.fig and Profile.tif file.

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PRACTICE

Create a figure (Figure 2) that shows the meteorological conditions in the period of interest by following the instructions in

the “meteo.m” script. It should include 2 subplots for a) wind speed c) wind direction

Plot wind speed with a continuous lines and wind direction with dots. Choose the line and marker sizes, axis label and ticks that

you find more suitable to obtain an effective plot. Use the function datetick to label the x axis with a data format

Once the figure has been created, modify the dimension of the plot, fix the resolution of the figure as 300 dpi and save the

figures both as Meteo.fig and Meteo.tif file.

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contour(X,Y,Z,v)

contour(X,Y,Z) draw contour plots of Z using X and Y to determine the x- and y-axis limits. It is possible to specify contour levels in the monotonically increasing vector v. The number of contour levels is equal to length(v).

A contour plot displays isolines of matrix Z.


contourf(X,Y,Z,v)

contourf(X,Y,Z) draws a filled contour plot of matrix Z. colormap(jet) sets the colormap to the matrix according to a certain built-in Matlab colorbar colorbar isplays the current colormap in the current figure caxis([cmin cmax]) sets the color limits to specified minimum and maximum values. Data values less than cmin or greater than cmax map to cmin and cmax, respectively.

4. DATA PLOTTING

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quiver(x,y,u,v)


4. DATA PLOTTING

Quiver A quiver plot displays velocity vectors as arrows with components (u,v) at the points (x,y). quiver(...,scale) automatically scales the arrows to fit within the grid and then stretches them by the factor scale.

streamline(X,Y,U,V,startx,starty)

Streamline draws streamlines from 2-D vector data. The arrays X, Y, which define the coordinates for U, V, must be monotonic, but do not need to be uniformly spaced. X, Y, must have the same number of elements, as if produced by meshgrid. startx, starty define the starting positions of the streamlines

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PRACTICE

Create a figure (Figure 3) that shows the temperature field as a function of time and depth, drawing a contour line every 1°C.

Follow the “contour.m” script as a guide. Depth is in y axis, time is in the x axis and the color refers to the temperature values. The vertical axis must be limited between 0 and 50m and spaced every

5m and must have “z (m)” as label. The horizontal axis must be limited between 01/08 to 10/08, be spaced every day and have

“time” as label. Use the function datetick to label the x axis with a data format. Add the grid , the title and the colourmap.

Once the figure has been created, fix the resolution of the figure as 300 dpi and save the figures both as Meteo.fig and Meteo.tif

file.

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LET’S PRACTICE

Through a numerical model, we set up a simulation of the entrance of Oglio river (Q=50m3/s; T = 15°C) in Lake Iseo during the

stratified season. The river’s plume intrudes at about 10m depth. Accordingly, we have extracted the velocity field (u and v

components) at -10m depth. The matrixes in the Inflow_path.mat file include: the x and y coordinates, the u and y components of

the velocity and the lake depth z for each point of the grid. Load the data and create a figure (Figure 4) that shows the

contour of the water speed (vel) superimposed to the velocity vector field, following the “inflow.m” script. Choose the scale of

the vector that assures a good visibility of the velocity field. Superimpose the streamline traced from the Oglio inlet and zoom

the figure in the area around the Oglio inlet. Save the figure

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4. DATA PLOTTING

surf(X,Y,Z)

Surf(X,Y,Z) uses Z for the color data and surface height. X and Y are vectors or matrices defining the x and y components of a surface. If X and Y are vectors, length(X) = n and length(Y) = m, where [m,n] = size(Z).

plot3(X1,Y1,Z1)

plot3(X1,Y1,Z1,...), where X1, Y1, Z1 are vectors or matrices, plots one or more lines in three-dimensional space through the points whose coordinates are the elements of X1, Y1, and Z1.

quiver3(x,y,z,u,v,w)

quiver3(x,y,z,u,v,w) plots vectors with components (u,v,w) at the points (x,y,z). The matrices x,y,z,u,v,w must all be the same size and contain the corresponding position and vector components.

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PRACTICE

Use the previous data to create a figure (Figure 5) that shows the bathymetry of lake Iseo superimposed to the Oglio vectors

located at -10m depth

data plotting with matlab - unibs.it · 1. why matlab? why matlab? matlab is a high-level...

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