Question

MATLAB help?
I figure out part 1..
1. You’re driving to California, and start at a green light at a velocity of 0 mph. Every 2 seconds your
velocity increases by 5 mph. You will reach maximum velocity at t = 60 seconds.
a. Create an array for time and an array for velocity.
b. Plot the velocity vs. time and label the axes.

2. If Statement: You see a sign for traffic cameras before starting and the maximum speed limit is 75
mph! Create an “if statement” within a “for loop” that will change any velocities above 75 mph to 75
mph. Plot the new velocity vs. time plot. This is how you will

Answer 1

this is what I got for #1

Answer 2

All I have to do is add a for loop that checks the velocity array. If any of the numbers in the velocity array are above 75, then it changes that number to 75. The graph will look similar, except it will go straight across once the velocity hits 75.


but, i dont know how to do this ^... help???

Answer 3

@jim_thompson5910 help? please ;/

Answer 4

you would add


[m,n] = size(v);

max = 75;

for i = 1:1:n
if( v(i) > max )
max = v(i);
end
end


This basically loops through the vector v (the velocity vector) and it tests to see if any elements in this vector are larger than 75 (the max). If there are any, then the max gets updated to this larger value. If not, then the max remains at 75.


note: [m,n] = size(v) gets the size of v which is a 1 x n matrix (matlab looks at everything like a matrix...even vectors)

Answer 5

do I need to define any variables before adding that ^. Also, do i add it to the end or anywhere in specific?

Answer 6

let me open up the doc, one sec

Answer 7

okay.

Answer 8

when you say "then it changes that number to 75"

what do you mean by "that number" ?

Answer 9

where do you see that?

Answer 10

you wrote in a post above


"All I have to do is add a for loop that checks the velocity array. If any of the numbers in the velocity array are above 75, then it changes that number to 75. The graph will look similar, except it will go straight across once the velocity hits 75. but, i dont know how to do this ^... help???"

Answer 11

So, you know how in the document, there are numbers that are above 75mph?

Answer 12

yes

Answer 13

in the velocity array

Answer 14

I need a loop that will change any of those "above 75mph" numbers back to 75 mph.

Answer 15

oh so something like 140 will change to 75 ?

Answer 16

yeah. because for number 2 any velocity over 75mph is not allowed, 75 mph is the max

Answer 17

ok one sec

Answer 18

[m,n] = size(v);

for i = 1:1:n
if( v(i) > 75 )
v(i) = 75;
end
end

This loops through the vector v and it changes any value over 75 to 75.

The vector v is really a matrix of size 1 x n (1 row, n columns)

Answer 19

where do i add it?

Answer 20

before you use the vector v (so before you plot the graph of the velocities)

Answer 21

so before..

V=A*t%find the velocity as a function of time

Answer 22

no, that's how you find all the velocities

if you do it before that line, it will be working with a blank or undefined array

Answer 23

so after that line, but before you use it to plot

Answer 24

it says undefined variable of 'v'.

Answer 25

when i put [m,n]=size(v);

Answer 26

you're using capital V

Answer 27

i think it's case sensitive

Answer 28

so try [m,n] = size(V);

Answer 29

yeah i got it, lol my mistake. but now its not wanting to end show the data.

Answer 30

what do you mean

Answer 31

GOT IT ;D thank you so much!

Answer 32

ok great, yw