The use of Sum()

I am not sure how to use the sum command can any one help me understand what I am doing wrong?

[per isakson]

I suspect that the error messages are not thrown by the code shown in the image. The image doesn't have the line x(1) = 1:9; However, you cannot assign a vector to a scalar.

>> x = nan(1,4);
>> x(1) = 1:9;
Unable to perform assignment because the left and right sides have a different number of elements. 

and sum cannot operate on a line object

>> L=line([1;2],[3;4])
L = 
  Line with properties:

              Color: [0 0.4470 0.7410]
          LineStyle: '-'
          LineWidth: 0.5000
             Marker: 'none'
         MarkerSize: 6
    MarkerFaceColor: 'none'
              XData: [1 2]
              YData: [3 4]
              ZData: [1×0 double]

  Show all properties
>> 

And see Debug a MATLAB Program and Examine Values While Debugging

[Walter Roberson]

line() is only for drawing lines on the display.

You are passing in [x(1); x(9)] for the x component and [y(1); y(9)] for the y component, and you are doing that no matter what the value of i is. It is questionable what x(9) and y(9) are going to hold before you assign to x(i) and y(9) when i reaches 9. Effectively you are going to draw only two different lines: the same line for i = 1 to 8, and then a second different line when i reaches 9 so you overwrite x(9) and y(9), and the second line will be repeated for the remainder of the i iterations. It is not obvious why you are doing this.

[Nishant Gupta]

Hi Joshua

First of all you cannot pass a line to the sum( ) function and can you send me the full code script so that I can help you further.

Answer 1

[Nishant Gupta]

Hi Joshua

Like I previously mentioned in my comment, you cannot pass a line to the "sum( )" function. From the code it seems that you are trying to calculate the area under the given curve which is basically integration.

Refer to the following modified code script, it will help you :

x(1)= 0;
x(n)= 1;
h= 0.001;
n = (x(n) - x(1))/h;
area = 0;
sum1 = 0;
 
for i=1:n
       x(i + 1) = x(i) + h;
       y(i) = -9 * exp(-10 * x(i)) + 18 * exp(-15 * x(i))
       area = y(i) * h;
       sum1 = sum1 + area;
end

For better accuracy, I have decreased the step size "h" to 0.001

As a second alternative, you can directly use the integral function referred in the following link:

https://www.mathworks.com/help/matlab/ref/integral.html