 # JavaScript: Check whether a given matrix is lower triangular or not

## JavaScript Basic: Exercise-121 with Solution

Write a JavaScript program to check whether a given matrix is lower triangular or not.

Note: A square matrix is called lower triangular if all the entries above the main diagonal are zero.

Sample Solution:

HTML Code:

``````<!DOCTYPE html>
<html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title> Check whether a given matrix is lower triangular or not</title>
<body>

</body>
</html>
```
```

JavaScript Code:

``````function lower_triangular_matrix(user_matrix) {
for (var i = 0; i < user_matrix.length; i++)
{
for (var j = 0; j < user_matrix.length; j++)
{
if (j > i && user_matrix[i][j] !== 0)
return false;
}
}
return true;
}

console.log(lower_triangular_matrix([[1, 0, 0],[2, 0, 0], [0, 3, 3]]));
console.log(lower_triangular_matrix([[1, 0, 1],[2, 0, 0], [0, 3, 3]]));
``````

Sample Output:

```true
false
```

Flowchart: ES6 Version:

``````function lower_triangular_matrix(user_matrix) {
for (let i = 0; i < user_matrix.length; i++)
{
for (let j = 0; j < user_matrix.length; j++)
{
if (j > i && user_matrix[i][j] !== 0)
return false;
}
}
return true;
}

console.log(lower_triangular_matrix([[1, 0, 0],[2, 0, 0], [0, 3, 3]]));
console.log(lower_triangular_matrix([[1, 0, 1],[2, 0, 0], [0, 3, 3]]));
``````

Live Demo:

See the Pen javascript-basic-exercise-121 by w3resource (@w3resource) on CodePen.

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## JavaScript: Tips of the Day

Parameter's value

```function getItems(fruitList, ...args, favoriteFruit) {
return [...fruitList, ...args, favoriteFruit]
}

getItems(["banana", "apple"], "pear", "orange")
```

...args is a rest parameter. The rest parameter's value is an array containing all remaining arguments, and can only be the last parameter! In this example, the rest parameter was the second parameter. This is not possible, and will throw a syntax error.

```function getItems(fruitList, favoriteFruit, ...args) {
return [...fruitList, ...args, favoriteFruit];
}

getItems(['banana', 'apple'], 'pear', 'orange');```
The above example works. This returns the array [ 'banana', 'apple', 'orange', 'pear' ].

Ref: https://bit.ly/3jFRBje