How to feed a function's output later on?
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stavanger
el 17 de Ag. de 2014
Comentada: stavanger
el 19 de Ag. de 2014
I need to assign output to a function through a program not when I define the function. For example f(.2,-.5)=4 and in a few line later f(-3,4.5)=-5. This is going to save other function's output. It's important that indices to be non-integer and negative so I cannot use a matrix for saving these date. How can I do this? Thanks in advance.
4 comentarios
John D'Errico
el 17 de Ag. de 2014
Store the values of [x,y,f(x,y)] in one array, as rows (or columns) of an Nx3 or 3xN array.
What is the problem? If you have something special that you need, you need to be more explicit.
Respuesta aceptada
Iain
el 18 de Ag. de 2014
I reckon this will do it:
function z = f(x,y)
persistent old_x old_y old_z
if isempty(old_x)
old_x = x;
old_y = y;
z = calculate the answer
old_z = z;
else
z = old_z(x == old_x & y == old_y);
if isempty(z) % old result doesn't exist, need to recalculate
old_x(end+1) = x;
old_y(end+1) = y;
z = calculate the answer
old_z(end+1) = z;
end
5 comentarios
Iain
el 19 de Ag. de 2014
persistent old_x old_y old_z
What that does is, it says to the function "remember these values the next time you get run, to save time".
The first if statement determines if the code has been run before. If not, it just calculates the result, and updates old_x, old_y and old_z with the new result.
If it has run before, it attempts to read an old answer
z = old_z(x == old_x & y == old_y);
If it couldn't read an answer, it calculates the answer and updates old_x, old_y and old_z with the new result.
old_x(end+1) = x;
That means append the value of x to the "old_x" vector.
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Adam
el 18 de Ag. de 2014
By the sounds of it some kind of encoding of your x and y values to a single key is what you need. This key can then be used with the corresponding f(x,y) result in a
containers.Map
object.
If you are familiar with maps in C++ or some other language Matlab maps can seem a bit strange, but they are good for this type of thing if your x and y values are not of a contiguous variety that could easily form the rows and columns of a 2d matrix.
What is the best way to encode an (x,y) pair into a single key to provide a map lookup for that value though depends on the range of your x and y values. I'm certainly not an expert on encoding data into keys, but for just 2 values it should be quite simple to find an encoding that ensures uniqueness for every valid (x,y) pair.
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