5 Functions and Files.pdf
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MATLABFunctions and Files
Cheng-Liang ChenPSELABORATORY
Department of Chemical EngineeringNational TAIWAN University
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Chen CL 1
Using Files filename1.m
Used for MATLAB programs and for some MATLAB functions M-files are ASCII (American Standard Code for Information Interchange)
files that are written in the MATLAB language(Can be created using any word processor or text editor)
filename2.mat
Used to save the names and values of variables created during aMATLAB session
MAT-files arebinaryfiles (more compact storage thanASCIIfiles) readable only by the software that created them
ASCII Data Files Header: comments describing what the data represents, the date it was
created, who created the data . . . One or more lines of data
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Chen CL 2
Controlling Input and Output
speed = 63;disp(The predicted speed is:)
disp(speed)
The predicted speed is:
63
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Chen CL 3
Input/Output Commands
Command Description
disp(A) Displays the contents, but not the name, of thearray A.
disp(text) Displays thetext stringenclosed within single quotes.
format Controls the screens output display format (Table3.3-2).
fprintf Performs formatted writes to the screen or to a file (seeAppendix C).
x=input(text) Displays thetextin quotes, waits for user input from thekeyboard, and stores thevalue in x.
x=input(text,s) Displays thetextin quotes, waits for user input from thekeyboard, and stores the input as a string in x.
k=menu(title,option1,option2,...)
Displays a menu whose title is in the string variable title,and whose choices are option1,option2,. . .
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Chen CL 4
Ex: Design of A Parallel-plate CapacitorCapacitors are widely used in electric circuits. A capacitor stores energy bymaintaining the charge separation produced when a voltage is applied to thedevice. A parallel-plate capacitor is constructed from two or more parallelconducting plate, each having anarea A and separated from each other by air oranother dielectric material such as mica or paper. If the plates are separated by adistanced, the devicescapacitance C, which is a measure of its energy storagecapacity, can be computed from the formula
C= (n 1) Ad
where n is the number of platesand is the permittivity of the dielectric material.
The unit of capacitance is thecoulomb/voltand is called thefarad(F). Suppose
we use plates having an area A= 20 centimeters2, separated by a distance d= 4
millimeters with air, for which= 8.85 1012 farad/meter. Construct a table toselect the number of plates needed to obtain a desired capacitance value. Assume
that no more than 10 plates will be used.
C C
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Chen CL 5
Ex: Design of A Parallel-plate Capacitor% Program capacitor.m
% Generates a table of capacitance values.
%
% Define the values of the constants.
permittivity = 8.85e-12;
A = 20/100^2; % Convert A to square meters
d = 4/1000; % Convert d to meters
%
n = [2:10]; % Vector n is # of plates% Generates capacitance values
% (Multiply by 10^12 for
% display purposes)
C = ((n-1)*permittivity*A/d)*1e12;
%
table(:,1) = n; % Create first columntable(:,2) = C; % Create second column
% Display table heading
% and table itself.
disp(No. Plates Capa.(F)xe12)
disp(table)
No. Plates Capa.(F)xe12
2.0000 4.4250
3.0000 8.8500
4.0000 13.27505.0000 17.7000
6.0000 22.1250
7.0000 26.5500
8.0000 30.9750
9.0000 35.4000
10.0000 39.8250
Ch CL 6
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Chen CL 6
Numeric Display Formats
Command Description and Example
format short Four decimal digits (the default);13.6745
format long 16 digits; 17.27484029463547
format short e Five digits (four decimals) plus exponent;6.3792e+03
format long e 16digits (15decimals) plus exponent;6.379243784781294e-04format bank Two decimal digits; 126.73
format + Positive, negative, or zero; +
format rat Rational approximation;43/7
format compact Suppresses some line feeds
format loose Resets to less compact display mode
Ch CL 7
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Chen CL 7
User Input
TheInput function displays text on the screen, waits for the user
to enter something from the keyboard, and then stores the inputin the specified variable
x = input(Please enter the value of x: )
Calender = input(Enter the day of the week: , s)
k = menu(title, option1, option2,...)
Demo the following in the class:
k = menu(Choose a data marker, o, *,x);type = [o, *,x];
x = [1,2,3,4]; y = [2,4,3,5];
plot(x,y, x,y, type(k),LineWidth,2,MarkerSize,3)
set(gca,LineWidth,2,FontSize,16)
title(Test the use of menu,FontSize,16)
Ch CL 8
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Chen CL 8
Test Your Understanding
T3.0-1 Write a script file to compute and display a table toconvert from radians to degrees. Use five values for the radian
angle: 1, 2, 3, 4,and5radians. Be sure to label each column in the
table.
T3.0-2 The volume V of a sphere depends on its radius r asfollows: V = 4r3/3. Write a script file to compute and display
a table showing the volume in cubic meters versus the radius in
meters, for1 r 2, in increments of0.1. Label each column.
T3.0-3 The surface area A of a sphere depends on its radius r as
follows: A = 4r2. Write a script file that prompts the user to
enter a radius, computes the surface area, and displays the result.
Ch CL 9
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Chen CL 9
Some Common Mathematical FunctionsExponential
exp(x) Exponential; ex
sqrt(x) Square root;xLogarithmic
log(x) Natural logarithm;ln(x)
log10(x) Common (base10) logarithm; log(x) = log10(x)
Complex
abs(x) Absolute value;xangle(x) Angle of a complex numberx
conj(x) Complex conjugate
imag(x) Imaginary part of a complex numberx
real(x) Real part of a complex number x
Numericceil(x) Round to the nearest integer towardfix(x) Round to the nearest integer toward zero
round(x) Round toward the nearest integer
sign(x) Sigmum function: +1 ifx >0; 0 ifx= 0;1 ifx
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Chen CL 10
Complex Number Functions
x = - 3 + 4 i ;
y = 6 - 8 i ;mag_x = abs(x)
mag_x =
5.0000
mag_y = abs(y)
mag_y =
10.0000
mag_product = abs(x*y)50.0000
angle_x = angle(x)
angle_x =
2.2143
angle_y = angle(y)
angle_y =
-0.9273
sum_angles = angle_x + an
sum_angles =
1.2870
angle_product = angle(x*y
angle_product =
1.2870
Chen CL 11
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Chen CL 11
Test Your Understanding
T3.1-1For several values ofx and y, confirm that ln(xy) = ln x+ ln y.
T3.1-2
Find the magnitude, angle, real part, and imaginary part of the
number 2 + 6i.
Chen CL 12
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Chen CL 12
Trigonometric Functions
Trigonometric
cos(x) Cosine; cos x
cot(x) Cotangent; cot x
csc(x) Cosecant; csc x
sec(x) Secant; sec x
sin(x) Sine; sin x
tan(x) Tangent; tan xInverse trigonometric
acos(x) Inverse cosine;cos1x
acot(x) Inverse cotangent;cot1x
acsc(x) Inverse cosecant;csc1x
asec(x) Inverse secant; sec1x
asin(x) Inverse sine;sin1x
atan(x) Inverse tangent;tan1x
atan2(y,x) Four-quadrant inverse tangent
Chen CL 13
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Chen CL 13
Test Your Understanding
T3.1-3For several values ofx, confirm that eix = cos x+i sin x.
T3.1-4
For several values of x in the range 0
x
2, confirm that
sin1 x+ cos1 x= /2.
T3.1-5
For several values of x in the range 0 x 2, confirm thattan(2x) = 2 tan x/(1 tan
2
x).
Chen CL 14
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Chen CL 14
Hyperbolic functions
Hyperbolic
cosh(x) Hyperbolic Cosine; cosh x= (ex +ex)/2
coth(x) Hyperbolic Cotangent;cosh x/ sinh x
csch(x) Hyperbolic Cosecant;1/ sinh x
sech(x) Hyperbolic Secant;1/ cosh x
sinh(x) Hyperbolic Sine;sinh x= (e
x
ex
)/2tanh(x) Hyperbolic Tangent;sinh x/ cosh x
Chen CL 15
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Chen CL 15
Inverse Hyperbolic functions
Inverse hyperbolicacosh(x) Inverse hyperbolic cosine;
cosh1 x= ln(x+
x2 1), x 1acoth(x) Inverse hyperbolic cotangent;
coth1 x= 12
ln(x+1x1
), x >1 orx