ELI5: Explain Like I'm 5

Nabla symbol

The nabla symbol, which looks like an upside-down triangle (∇), is an important symbol in mathematics. It is used to indicate a mathematical operation called the "gradient". Let's break it down and understand it step by step.

Imagine you are on a very hilly landscape, with mountains and valleys. If you were to walk around on this landscape, you would experience changes in height. The gradient is a way to measure how steep these changes are.

Now, let's say you want to find out how steep the landscape is at a particular point. You would take the nabla symbol (∇) and put it in front of a function that tells you the height at any given point on the landscape. The nabla symbol acts like a special tool that helps you find this information.

The nabla symbol has three parts: ∇x, ∇y, and ∇z. These parts represent the directions in which we want to measure the steepness. The x part measures the steepness in the horizontal direction, the y part measures it in the vertical direction, and the z part measures it in the depth or third dimension.

When you apply the nabla symbol to a function, it calculates how much the function changes in each direction. It gives you three numbers: how much the function changes when you move left or right (∇x), how much it changes when you move up or down (∇y), and how much it changes when you move forward or backward (∇z).

These numbers can tell you a lot about the landscape. If the numbers are all small, it means the landscape is relatively flat and there are no big changes in height. If the numbers are large, it means there are steep slopes or sharp changes in height.

The nabla symbol is used in many areas of mathematics, including calculus and physics. It helps us understand how things change and how steep things are in different directions. So, the next time you see the nabla symbol (∇), remember that it's like a special tool to measure the steepness of a landscape or any other mathematical function.