MATLAB Short Course
2. Simple Mathematics
Assignment statements.
The preceding MATLAB commands that assign the value of the expression after the ’=’ sign to the variable before the ’=’ sign are assignment statements. Note that all variables in the expression after the ’=’ sign must have previously been allocated a value, or else an error occurs. For example, enter the following commands:
c=sqrt(a^2+b^2)
You will see the error message ??? Undefined function or variable ’b’ . Consider the following:
The last line has nothing at all to do with a mathematical equation. It is a MATLAB assignment statement that calculates x 2 −12 at x = 7 and stores the result in the variable x , thereby over-writing the previous value.
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Introduction to matlab programming.
Often, a result of some calculation is needed for later use, or perhaps a complicated expression can be examined more carefully if done in parts. Both can be done by the use of “variables”. Variables hold whatever result you put in them by the use of the equal sign ( = ):
- x=1 creates a variable called “x” and stores the value “1” in it. If one then types “x” in an expression , MATLAB® will use the value stored in “x”, i.e., “1”.
- Similarly one can define variables to hold anything that MATLAB can calculate.
- You can easily overwrite a variable with a new assignment: x=2 now the variable x “contains” the value “2”.
- One can use x as part of an expression: x^2+x-cos(x)
- Or to create a new variable: y= x^2+7
- A variable can be a vector (or matrix): A= [1 2 3 4]
- One can change just a part of A : A(3)= 0
In this last example, we are getting ahead of ourselves by referring to an element of a vector. We will touch on that more later.
Note that you can “hide” important MATLAB functions and constants by defining a variable with the same name: pi=3 will give interesting results later (to remove clear pi ). This is usually not a good idea, so take care before using a nice name like sum , exp , or det , as these are all built-in functions. You can check if a variable is already in use by using the which command:
tells us that pi is a built-in function, while
tells us that Pi is unused. The difference is in the capitalization. MATLAB-defined functions will always use lower-case names (even if the helpfile will show these as all CAPITAL), which implies that you can always avoid collision by capitalizing the fiirst letter of your variable and functions names.
- Let x=1 and y=2 . Exchange the values of these two variables without specifically using ‘1’ or ‘2’ i.e., the exchange should work regardless of the values held by the variables. Hint: You can invent a new variable. Another Hint: Imagine you have misplaced your kids’ breakfast and now Tom’s Cornflakes are in Sally’s bowl and Sally’s CocoPuffs are in Tom’s bowl. You have already poured the milk, how can you fix the problem without throwing away and starting over?
- Repeat some of the previous exercises using variables.
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2.8. Assignment Statement
General form of an assignment statement is given as follows:
When an assignment statement is executed, the value of the expression to the right of the equality sign is first computed and the result obtained is assigned to the variable mentioned on the left of the equality sign.
Example 2.5.
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1.4.1: More About Valid Variable Names
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- Page ID 87272
- Carey Smith
- Oxnard College
Variable Name Rules
MATLAB variable names must start with a letter. The rest of the name can be letters, numbers or the underscore symbol. The letters can be upper or lower case. These are valid variable names:
b, B, Basketball, Basket_Ball, basket5ball, basketBall_12345
These are not valid names:
Basket-Ball, Basket_Ball!, Basket?Ball, Basket Ball.
Descriptive names are encouraged, in order to make the code readable. So 'pressure' and 'press' are better names than just 'p'. Names are allowed to be very long, but they should not be more than a quarter of the command window, so keep them to less than 20 letters, unless there is a very good reason to make them longer. (The maximumn allowed name length is 63 characters.)
Sometimes, you may have 2 version of the same quantity, such as a distance in both inches and centimeters. A good practice is to give them related names with identifiers, such as dist_inch and dist_cm, so that you always know which units you are using.
Variable Names to Avoid
Don't use the name of a function. For example, don't use these names:
sqrt, sin, cos, log10, sum.
Also, don't use 2 names that only differ for upper vs. lower case letters; that can lead to confusion. For example, having 2 variables named kg and Kg should be avoided.
Exercise \(\PageIndex{1}\) Good Variable Names
Which of the following are good variable names? Make a decision about each before looking at the answers.
You may enter each in the command window by setting the name = 1, in order to see if it is valid.
You may use the exist() function to see if it is a function name.
A-very_long_name
Even_123_longer456_name_9876543210
sind -- a function name--don't use it
sinx -- valid
A-very_long_name -- not valid becuz of the -, which is interpreted as a minus sign
Even_123_longer456_name_9876543210 -- valid
important! -- nor valid becuz of the !
_next -- not valid. It can't start with an underscore
1one1 -- not valid. It can't start with a number
MATLAB keywords
It is not allowed to use MATLAB keywords. These are words that MATLAB reserves for program structure. This is the list of keywords:
'break' 'case' 'catch' 'classdef' 'continue' 'else' 'elseif' 'end' 'for' 'function' 'global' 'if' 'otherwise' 'parfor' 'persistent' 'return' 'spmd' 'switch' 'try' 'while'
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Logical (Boolean) Operations
MATLAB ® represents Boolean data using the logical data type. This data type represents true and false states using the numbers 1 and 0 , respectively. Certain MATLAB functions and operators return logical values to indicate fulfillment of a condition. You can use those logical values to index into an array or execute conditional code. For more information, see how to Find Array Elements That Meet a Condition .
This example shows how to filter the elements of an array by applying conditions to the array.
This example shows how to use the any and all functions to reduce an entire array to a single logical value.
Precedence rules determine the order in which MATLAB evaluates an expression.
Related Information
- MATLAB Operators and Special Characters
MATLAB Command
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Run the command by entering it in the MATLAB Command Window. Web browsers do not support MATLAB commands.
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IMAGES
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To assign values in the MATLAB base workspace, use 'base'. The base workspace stores variables that you create at the MATLAB command prompt, including any variables that scripts create, assuming that you run the script from the command line or from the Editor. To assign variables in the workspace of the caller function, use 'caller'. The caller ...
You can create new variables in the workspace by running MATLAB code or using existing variables. To create a new variable, enter the variable name in the Command Window, followed by an equal sign (=) and the value you want to assign to the variable. For example, if you run these statements, MATLAB adds the four variables x, A, I, and C to the ...
Assignment of variables by comma separated lists. Learn more about variables MATLAB. ... which states "You also can enter more than one statement on the same line by separating statements. To distinguish between commands, end each one with a comma or semicolon. Commands that end with a comma display their results, while commands that end with a ...
Assignment Statements. You can create your own variables, and give them values, with an assignment statement. The assignment operator is the equals sign (=), used like so: >> x = 6 * 7 x = 42. This example creates a new variable named x and assigns it the value of the expression 6 * 7. MATLAB responds with the variable name and the computed value.
Assignment Statement. An assignment statement is used to assign a value to a variable name. Once the value has been assigned, the variable name can be used instead of the value. Matlab allows a variable to be assigned to a single scalar value, or an array of values. You will learn more about arrays in later lessons. The = sign is the assignment ...
The preceding MATLAB commands that assign the value of the expression after the '=' sign to the variable before the '=' sign are assignment statements. ... It is a MATLAB assignment statement that calculates x 2 −12 at x = 7 and stores the result in the variable x, thereby over-writing the previous value. Previous.
This video explains the definition of variable assignment in MATLAB and what is the rules to name a variable in MATLAB. In addition, How to defined multiple ...
In MATLAB, an assignment statement automatically generates variable. Assign the value to a Variable. An assignment statement used for assigning a value to a variable. The assignment statement generally having the symbol = which is known as the assignment operator. Example: The statement in MATLAB is given as. x=10; fprintf('%d\n',x) Output: 10 ...
So the following works as expected: > [x,y] = deal(88,12) x = 88. y = 12. The syntax c{:} transforms a cell array in a list, and a list is a comma separated values, like in function arguments. Meaning that you can use the c{:} syntax as argument to other functions than deal. To see that, try the following:
If one then types "x" in an expression, MATLAB® will use the value stored in "x", i.e., "1". Similarly one can define variables to hold anything that MATLAB can calculate. You can easily overwrite a variable with a new assignment: x=2 now the variable x "contains" the value "2". One can use x as part of an expression: x^2+x ...
Variable Assignment. This works just like storing values as variables on your calculator, except it is much easier with MATLAB (and a full keyboard). We say that the variable x has been assigned the value 42, or that the value 42 is now "stored in x ". Notice that a new entry has appeared in the workspace corresponding to this variable assignmetn.
You can assign any or all consecutive elements of a comma-separated list to variables with a simple assignment statement. Define the cell array Cand assign the first row to variables c1 through c6. C = cell ... MATLAB assigns C{1,1:3} to the variables c1, c2, and c3 and ignores C{1,4:6}.
2.8. Assignment Statement General form of an assignment statement is given as follows: variable_name = expression; When an assignment statement is executed, the value of the expression to the right … - Selection from MATLAB® and Its Applications in Engineering: [Based on MATLAB 7.5 (R2007b)] [Book]
Variable Name Rules. MATLAB variable names must start with a letter. The rest of the name can be letters, numbers or the underscore symbol. The letters can be upper or lower case. These are valid variable names: b, B, Basketball, Basket_Ball, basket5ball, basketBall_12345. These are not valid names:
Conditional Statements. Conditional statements enable you to select at run time which block of code to execute. The simplest conditional statement is an if statement. For example: % Generate a random number. a = randi(100, 1); % If it is even, divide by 2. if rem(a, 2) == 0. disp('a is even')
23. One line conditional assignment: a(a > 5) = 2; This is an example of logical indexing, a > 5 is a logical (i.e. Boolean or binary) matrix/array the same size as a with a 1 where ever the expression was true. The left side of the above assignment refers to all the positions in a where a>5 has a 1.
MATLAB ® represents Boolean data using the logical data type. This data type represents true and false states using the numbers 1 and 0, respectively. Certain MATLAB functions and operators return logical values to indicate fulfillment of a condition. You can use those logical values to index into an array or execute conditional code.