Question

Write an M-file to evaluate the equation $y(x)=x^2-3x+2$ for all values of $x$ between $0.1$ and 3 , in steps of $0.1$. Do this twice, once with a for loop and once with vectors. Plot the resulting function using a 3 point thick dashed red line.

Short answer

Create an M-file and define 'x' values using linspace. Evaluate the equation $y(x)=x^2-3x+2$ for each 'x' value using a for loop and store results in 'y_for'. Next, evaluate the equation using vectors and store results in 'y_vec'. Plot the function with a 3 point thick dashed red line, label axes and title, and enable the grid. Finally, save and run the script to display the resulting plot.

Step-by-step solution

Define x values using linspace

In the script, define the x values between 0.1 and 3 with an increment of 0.1: ``` x = linspace(0.1, 3, (3-0.1)/0.1); ``` Step 3: Evaluation using for loop

Evaluate equation using for loop

Use a for loop to evaluate the equation for each x value and store the result in a new array 'y_for': ``` y_for = zeros(size(x)); for i = 1:length(x) y_for(i) = x(i)^2 - 3*x(i) + 2; end ``` Step 4: Evaluation using vectors

Evaluate equation using vectors

Now, evaluate the equation using vectors and store the result in a new array 'y_vec': ``` y_vec = x.^2 - 3.*x + 2; ``` Step 5: Plotting the function

Plot the function with a dashed red line

Plot the function with a 3 point thick dashed red line. Since the results from the for loop and vectors are the same, we can use any of the y arrays for plotting: ``` plot(x, y_for, 'r--', 'LineWidth', 3); xlabel('x'); ylabel('y(x)'); title('y(x) = x^2 - 3x + 2'); grid on; ``` Step 6: Save and run the script Save the 'FunctionEvaluation.m' script and then run it in the MATLAB environment. The resulting plot will display the evaluated function as a dashed red line.

Key concepts

For Loop in MATLAB

A "for loop" in MATLAB is a basic programming construct that allows you to repeat a group of commands a specific number of times. This is particularly useful when you need to perform repetitive calculations, like evaluating a function at multiple points. For loops in MATLAB are defined by specifying the range of iterations and the block of code to be executed during each iteration.

To demonstrate, consider the equation we'll evaluate: $y(x)=x^2-3x+2$. Using a for loop, we can iterate over our defined range of x values from 0.1 to 3, with steps of 0.1. Here’s a closer look at the key points:

• Initialize the result array, `y_for`, to store output values.
• Write a loop that goes from $1$ to the length of the `x` array.
• During each iteration, calculate $y$ based on the equation and store it in `y_for`.

The for loop will evaluate $x(i{)}^2-3\ast x(i)+2$ for each $x(i)$, thus populating `y_for` with corresponding $y$ values.

Vectorization in MATLAB

Vectorization in MATLAB makes your code run faster and more efficiently by replacing explicit loops with vector operations. MATLAB is optimized for operations on arrays and matrices, so taking advantage of vectorized code often leads to better performance. Instead of iterating through each element manually, vectorization processes all elements at once using vectorized calculations.

For the same equation, $y(x)=x^2-3x+2$, vectorization allows for a cleaner and more concise code approach. Here's what vectorization looks like:

• Define `x` using `linspace` to create your vector of values.
• Apply the formula directly to the vector `x`, without using loops: `y_vec = x.^2 - 3.*x + 2`.

The above statement will perform the calculations on every element of `x` simultaneously. This not only simplifies the code but also capitalizes on MATLAB's strengths in handling array operations.

Plotting in MATLAB

Plotting in MATLAB is a straightforward way to visualize data, allowing you to see trends and patterns quickly. In this exercise, you need to plot the evaluated function $y(x)$ against `x` values from 0.1 to 3. MATLAB offers various options for customizing plots, making it a versatile tool for data visualization.

For our function, the plot is specified with a red dashed line that is 3 points thick. Here is how to achieve this using the `plot` function:

• Use the command `plot(x, y_for, 'r--', 'LineWidth', 3);` where `'r--'` denotes a red dashed line.
• Enhance the plot with labels using `xlabel('x')` and `ylabel('y(x)')` to clarify the axes.
• Add a title with `title('y(x) = x^2 - 3x + 2')`.
• Enable the grid using `grid on` for better readability of the plot.

Once you've set up the code, executing it will display the function on a graph, allowing for an easy and effective analysis of the evaluated mathematical expression.