# Options when using the ode23/45 solver

hi

I'm making a script for calculating ray paths in the subsurface using kinematic ray tracing.
To my disposition I have a velocity model given on a 2D grid.

I'm having troubles understanding how to use Options in order to specify the borders for when the ode23 function is supposed to stop(which is when it reaches the border of the grid).

At the moment i use the following:
[t,f] = ode23('raytrace', [0 10],[x0,z0,px0,pz0]);

function dz =raytrace(t,z)
global v dx dz

dz = zeros(4,1);
if z(2) < 0;
vel = interp2(3.5:0.01:20,0:-0.01:-10,v,z(1),z(2),'*linear');
v2 = vel^2;
v1 = 1/vel;
vx = interp2(3.5:0.01:20,0:-0.01:-10,dx,z(1),z(2),'*linear');
vz = interp2(3.5:0.01:20,0:-0.01:-10,dz,z(1),z(2),'*linear');
dz(1) = v2*z(3);
dz(2) = v2*z(4);
dz(3) = -v1*vx;
dz(4) = -v1*vz;
elseif z(2) > 0;
return
end
end

My goal is to not have to use the if/else if sentence in order to make it a bit more elegant.

Last edited:

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I'm aware that my first post was slightly unclear and it was not easy to understand what I meant.

I want to set an event so that when the ray I shoot reaches the surface Z = 0 the ODE function stops.

I also want to implement the event so that it stops if the ray travels outside the grid in the x direction.

I know I need to use the event function but I'm unable to comprehend how to use it even after reading examples.

I would really appreciate some help in this matter.