This section describes the functions to control the program flow.

Control Flow #

if #

Description
If the condition is true, executes statements.
Used in FDTD and FDE.

Syntax
(1) If the expression is true, executes statements.

if expression
    statements
end

or

if (expression){
    statements
}

(2) If the expression is true, executes statements_1. Otherwise, executes statements_2.

if  expression
    statements_1
else
    statements_2
end

or

if (expression){
    statements_1
}
else{
    statements_2
}

(3)If the expression_k is true, executes the statements_k.

if expression_1
    statements_1
elseif expression_2
    statements_2
...
elseif expression_k
    statements_k
else
    statements_k+1
end

or

if (expression_1){
    statements_1
}
elseif (expression_2){
    statements_2
}
...
elseif (expression_k){
    statements_k
}
else{
    statements_k+1
}

Example

if  0
    'true-1'
elseif 0
    'true-2'
elseif 1
    'true-3'
else
    'else-part'
end 

or

if  (0){
    'true-1'
}
elseif (0){
    'true-2'
}
elseif (1){
    'true-3'  
}
else{
    'else-part'    
}

Result:

val =
true-3

See also
while, for

while #

Description
While the expression is true, executes the statement.
Used in FDTD and FDE.

Syntax
While the expression is true, executes the statement.

while expression
    statement;
end

or

while (expression){
    statement;
}

Example

i = 0;
while i <= 5
    printf("i = %d\n", i);
    i = i + 1;
end

or

i = 0;
while (i <= 5){
    printf("i = %d\n", i);
    i = i + 1;
}

Result:

i = 0
i = 1
i = 2
i = 3
i = 4
i = 5

See also
if, for

for #

Description
Executes the statements for each element that meets the requirement.
Used in FDTD and FDE.

Syntax
Iterates over each element in a value set.

for element = values
    statements;
end

Executes statements based on explicit initialization, condition checking, and increment expressions.

for (init; condition; increment){
    statements;
}

Example

x = ["a", "sample", "string"];
for i = x
    printf ("%s ", i); 
end

or

x = ["a", "sample", "string"];
for (i = 1; i <= length(x); i = i + 1){
    printf("%s ", x(i));
}

Result:

a sample string 

See also
if, while

break #

Description
Breaks the for or while loop, the code after break sentence will not be executed.
Used in FDTD and FDE.

Syntax
Breaks the for or while loop.

break;

Example

for  i = 1:100
    
    if i == 3 
        break;
    end
    printf("i = %d\n", i);
end

Result:

i = 1
i = 2

See also
continue

continue #

Description
Terminates the current iteration and starts the next iteration of for or while loop.
Used in FDTD and FDE.

Syntax
The continue statement forces execution of the next iteration of the inner-most for or while loop to begin immediately.

continue;

Example

for  i = 1:4
    
    if i == 2
        continue;
    end
    printf("i = %d\n", i);
end

Result:

i = 1
i = 3
i = 4

See also
break

try, catch #

Description

The try and catch statements form a control flow construct for error handling.

The try statement defines a block of code that is tested for errors during execution. If an error is detected while executing commands within the try block, the try statement is immediately exited.

The catch statement defines a block of code to be executed when an error occurs. It is optional. If a catch block is present, the program automatically executes the commands in it when an error occurs.

Both syntax forms support nesting of try and catch.

Used in FDTD and FDE.

Syntax

Code	Function
try	Executes commands in the try block and checks errors.
catch	Catches the error messages from try block and processes error messages according to the catch block.

1. Execute the code block following try. If an error occurs, the try statement continues in one of two ways, and finally ends with end:

• No catch statement: exit the try statement and continue executing the script after end.
• A catch statement exists: when an error occurs, store the error message in the variable after catch (e.g., error_message), then execute the subsequent code block of catch (if any); if none, directly continue executing the script after end.

try
    commands;
end
...

# or
try
    commands_1;
catch error_message
    commands_2;
end

2. Execute the code block inside {} following try. If an error occurs, one of two cases applies:

• No catch statement: exit the try block and continue executing the script after the closing }.
• A catch statement exists: when an error occurs, store the error message in the variable inside the parentheses after catch (e.g., error_message), then continue executing the subsequent script.

try{
    commands;
}

# or
try{
    commands_1;
} 
catch(error_message)
commands_2;

Example

Example 1:

try
    a
catch err
    D = 4;
end
err

# or
try{
    a
} 
catch(err)
err
D = 4;

Result:

err = 
'a' is undefined function or variable

Example 2:

try
    x = 10;
    try
        y = z;
    catch inner_err
        inner = inner_err;
        inner
    end
end

# or
try{
    x = 10;
    try{
        y = z;
        } 
    catch(inner_err)
    inner = inner_err;
    inner
    }

Result:

inner = 
'z' is undefined function or variable

See also

if, while

Logic and Boolean Values #

and #

Description

and is a logical operator that returns true if both operands are true; otherwise it returns false. In the software, true is represented as 1 and false as 0.
Used for all solvers.

Syntax

Code	Function
expr1 and expr2	Logical AND. Returns 1 if both expr1 and expr2 are true; otherwise returns 0. Equivalent to expr1 & expr2.

Example

a = 1;
b = 2;
c = (a == 1 and b == 2);
d = (a == 0 and b == 2);
c
d

Result:

c = 
1
d = 
0

See also

or

or #

Description

or is a logical operator that returns true if at least one operand is true; it returns false only when both operands are false. In the software, true is represented as 1 and false as 0.
Used for all solvers.

Syntax

Code	Function
expr1 or expr2	Logical OR. Returns 1 if at least one of expr1 or expr2 is true; returns 0 only if both are false. Equivalent to expr1 | expr2.

Example

a = 0;
b = 2;
c = (a == 1 or b == 2);
d = (a == 1 or b == 0);
c
d

Result:

c = 
1
d = 
0

See also

and

true #

Description

true is a Boolean constant representing the logical value “true”. In the software, true is numerically represented as 1.
Used for all solvers.

Syntax

Code	Function
true	Returns the Boolean value true, which is equivalent to 1 in numeric contexts.

Example

flag = true;
flag

Result:

flag = 
1

See also

false

false #

Description

false is a Boolean constant representing the logical value “false”. In the software, false is numerically represented as 0.
Used for all solvers.

Syntax

Code	Function
false	Returns the Boolean value false, which is equivalent to 0 in numeric contexts.

Example

flag = false;
flag

Result:

flag = 
0

See also

true