Identifying a variable in a for loop

I'm trying to model the two dimensional motion of particles and I have the velocity data of the particles in the x- and y-directions. However, I am trying to use a for loop to move the particles through the geographic space, based on their velocities. The challenge I've run into is that in my for loop I am trying to use the equation x(i) = u(i-1)*dt, where x(i) is the current x-position and u is the x-velocity, and u is known at each x- and y-location. I want to be able to code that u(i) = u at x(i), referring to the data that i inported into matlab, but I'm unfamiliar with how to write that code.

I've attached the excel file here for reference. The x-position is long_E in the file, and the x-velocities are ve. The time series information is also included in the excel file.

Thanks for any suggestions you can offer. I'm still really new to using matlab and to coding in general.

[Mehmed Saad]

what do you mean by u(i) = u at x

• do you mean that you have u(i-1) corresponding to x(i) and you want to have u(i) corresponding to x(i)?
• do you mean you want the value u(i) in variable u?
• do you want to access time for that purpose?

[Aaron Ridall]

Hi, Muhammad. What I want to be able to do is run the forloop so that the code will assess the x and y position the particle is at in the timestep and then use the appropriate u-value (ve in the excel) for that x,y position and the time. U is a velocity, so if I multiply u by dt, then it will generate a distance the particle has moved in the horizontal x-direction and the change in x-direction (along with the change in y-position that will work in a similar way) will represent a new value for the velocities (u and v) that I should be using for the next time step.

[Mehmed Saad]

and you have to calculate dt from t ? taking difference between current and previous time

if yes, then take this for example

see the 2nd row of your data

x = -80.3780
u = -0.1801
t = datetime('01-Jan-2015 06:00:00')
dt = 21600; %seconds as 01-Jan-2015 00:00:00 - 01-Jan-2015 06:00:00 = 6Hrs
u_into_dt = u*dt

u_into_dt =

-3.8902e+03

I dont think this is right

can you give an example like that so that i can understand what you are trying to do