MATLAB PROGRAMMING

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MATLAB PROGRAMMING

• M-Files Editor
• M-Files scripts and functions
• Program Control Statements
• Types of Functions
• Calling Functions
• Optimizing for Speed
• Profiler
• Inline function
• Function Handles

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M-Files Editor
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M-Files scripts and functions
.m
Type of M-file

• MATLAB scripts
• Are useful for automating a series of steps
  you need to perform many times.
• Do not accept input arguments or return output
  arguments.
• Store variables in a workspace that is shared
  with other scripts and with the MATLAB command
  line interface.
• MATLAB functions
• Are useful for extending the MATLAB language
  for your application.
• Can accept input arguments and return output
  arguments.
• Store variables in a workspace internal to the
  function.

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Types of M-Files
M-file scripts

• Scripts share workspace with interactive MATLAB
  session and with other scripts.
• They operate on existing data in the workspace,
  or create new data on which to operate.
• Any variables that scripts create remain in the
  workspace after the script finishes
• Be aware that running a script can
  unintentionally overwrite data stored in the base
  workspace

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Types of M-Files
M-file functions

• Functions are program usually implemented in
  M-files, that accept input and return output
  arguments.
• They operate on variables within their own
  workspace which separate from the MATLAB base
  workspace .
• The variables that pass to a function must be in
  the calling context, and the function returns its
  output arguments to the calling workspace
  context. You can, however, define global
  variables explicitly, allowing more than one
  workspace context to access them.

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Basic Parts of an M-File
function f fact(n)
Function definition line Compute a
factorial value. H1 line
FACT(N) returns the factorial of N, Help
text usually denoted by N! Put simply,
FACT(N) is PROD(1N). Comment f prod(1n)
Function
body
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Program Control Statements
Loop Control - for, while, continue, break
1. for-end loop executes a predetermined number
of times. for index startincrementend
statements end 2. while-end loop
executes repeatedly as long as the controlling
expression is true. while expression
statements end If expression is a matrix, all
its elements must be true for execution to
continue.
for k matrix statements end
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Program Control Statements
3.Continue continue passes control to the next
iteration of for or while loop, skipping any
remaining statements in current loop. In nested
loops, continue passes control to the next
iteration of the for or while loop enclosing
it. 4. break break terminates the execution of a
for loop or while loop. When a break statement is
encountered, execution continues with the next
statement outside of the loop. In nested loops,
break exits from the innermost loop only.
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Program Control Statements
Conditional Control - if, switch

• 1. if-end-else, elseif
• if evaluates a logical expression, if logical
  expression is true, MATLAB executes all the
  statements between if and end lines.
• if logical_expression
• statements
• end
• else and elseif
• else has no logical condition, it execute when
  the preceding if (possibly elseif condition)
  evaluates to false.
• elseif has a logical condition, it evaluates if
  the preceding if (possibly elseif condition) is
  false. it execute when its logical condition
  evaluates to true.

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Program Control Statements
2. switch, case, and otherwise switch expression
(scalar or string) case value1
statements Executes if expression is
value1 case value2 statements
Executes if expression is value2 .
otherwise statements Executes if
expression does not
match any case end
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Program Control Statements
Error Control -- try, catch

• The statements between try and catch are
  executed until an error occurs. The statements
  between catch and end are then executed.
• Use lasterr to see the cause of the error.
• If an error occurs between catch and end,
  terminates execution unless another try-catch
  sequence has been established.

try statement ... catch statement
... end
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Program Control Statements
Other Statements-- return, pause,
input, keyboard
return terminates the current sequence of
commands and returns control to the invoking
function or to the keyboard. pause causes
M-files to stop and wait for pressing any key
before continuing. pause(n) pauses execution for
n seconds before continuing. keyboard when
placed in an M-file, stops execution of the file
and gives control to the keyboard. To terminate
the keyboard mode, type return input Request
user input
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Types of Functions
Primary M-File Functions The first function
in M-file is called primary function. Nested
Functions Functions defined within the body
of another function Subfunctions Any
functions that follow the primary function in an
M-file Private Functions Functions with
restricted access, callable only from an M-file
function in the parent directory Anonymous
Functions Functions defined from a expression,
without requiring an M-file Overloaded
Functions Functions with multiple
implementations that respond to different types
of inputs accordingly
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Calling Functions
1. Local Variables and Global Variables Local
Variables It be used only in function
scope Global Variables If you want more than one
function to share a variable, declare the
variable as global in all the functions. 2.
Function Syntax out functionname(in1, in2, ...,
inN) out1, out2, ..., outN functionname(in1,
in2, ..., inN) 3. Passing Arguments A pi
str1 'one' str2
'one' disp(A) Function syntax
strcmp(str1, str2) Function syntax 3.1416
ans
1
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Calling Functions

• 4. Arguments Numbers
• nargin returns number of input arguments
  specified for a function.
• nargout returns number of output arguments
  specified for a function.
• nargin(fun) returns the number of declared
  inputs for the function.
• nargout(fun) returns the number of declared
  outputs for the function.
• fun-may be the name of function or function
  handle.
• 5. Pass any number of inputs varargin
• Return any number of outputs arargout
• function varargout fun(n) returns a variable
  number of arguments
• from function
  fun.m.
• function y fun(varargin) accepts a variable
  number of arguments
• into function fun.m.

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Calling Functions
Programming Example Ploting the curves with
different damps Zeta0,0.3,0.707
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Optimizing for Speed

• You can save a preparsed version of a
  function or script, called P-code files .p, for
  later MATLAB sessions using the pcode function.
• pcode filename
• pcode filename inplace
• parses .m and saves the resulting pseudocode to
  the file .p. This saves MATLAB from reparsing
  .m the first time you call it.
• MATLAB is very fast at parsing so the pcode
  function rarely makes much of a speed difference.
• One situation where pcode does provide a speed
  benefit is for large GUI applications.
• Another situation for pcode is when you want to
  hide algorithms you've created in your M-file.

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Optimizing for Speed
Vectorizing CodeIt's best to avoid the use of
loops in programs that cannot benefit from
performance acceleration. Most loops can be
eliminated by performing an equivalent operation
using vectors instead. Coding Loops in a
MEX-File for SpeedIn this way, the loop executes
much more quickly since the instructions in the
loop do not have to be interpreted each time they
execute.
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Optimizing for Speed

• Preallocate to Improve PerformanceIt is much
  faster to preallocate a block of memory large
  enough to hold the matrix at its final size. For
  example, using zeros() or ones().
• Functions Are Faster Than Scriptsso, use
  function!
• Using build-in function
• Measuring Execution Time with tic and toc tic
• run the program section to be timed
• toc

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Optimizing for Speed

• JIT(Just In Time) Accelerator
• MATLAB performance enhancements are
  supported on a subset of MATLAB language
  capability.
• MATLAB accelerates code that uses the data types
  that are shaded in the class hierarchy diagram
  below

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Optimizing for Speed

• Performance acceleration applies to all MATLAB
  array shapes except for arrays having more than
  three dimensions.
• for Loops execute faster in MATLAB as long as
• Indices of the loop are set to a range of scalar
  values.
• Code in loop uses only the supported data types
  and array shapes.
• If the code in the loop calls any functions,
  they are built-in functions.
• if, elseif, while, and switch statements
  execute faster as long as the conditional
  expression evaluates to a scalar value.

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Profiler

• Profiler to help you improve the performance
  of M-files.

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Inline function
g inline(expr) g inline(expr,arg1,arg2,...) Us
ing char, class, argnames to see the information
of g. vectorize(inline_fun), fun is an inline
function object. The result is the vectorized
version of the inline function.
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Function Handles

• A function handle is a MATLAB value that
  provides a means of calling a function
  indirectly. You can pass function handles in
  calls to other functions or store function
  handles in data structures for later use.
• Constructing a Function Handle
• f_handle _at_functionname f_handle
  str2func(functionname) Handles to Anonymous
  Functions
• sqr _at_(x) x.2 The variable sqr contains
  a handle to this anonymous function.
• Arrays of Function Handles
• trigFun _at_sin, _at_cos, _at_tan
  trigFunstr2func(sin,cos,tan)
• Calling a Function Using Its Handle
• f_handle()
• Evaluate function
• y1,feval(f_handles, arg1,)
  y1,feval(funname, arg1,)

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Function Handles
Functions That Operate on Function Handles
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Function Handles
EXAMPLES