matlab - Undefined function or variable vector -

i'm using matlab , have loaded file contains variables date, ph , pressure_dbar (all vectors). i'm trying write function take in these variables, maximum , minimum pressure_dbar variables , return 2 new vectors: newdate , newph. want populate new vectors date , ph data if date , ph >= minimum , < maximum. below code, getting error "undefined function or variable" on newdate , newph. tried defining them outside of variable newdate = []; , newph = []; unsuccessful. tried different ways of iterating through vector, nothing. tips appreciated, thanks!

minimum = min(pressure_dbar); maximum = max(pressure_dbar);  function [newdate, newph] = oceanphdepth(date, ph, pressure_dbar, minimum, maximum)  = 1:length(date)     j = 1:length(ph)         if (ge(pressure_dbar, minimum) && lt(pressure_dbar, maximum))                 newdate = date(i);                 newph = ph(j);              end     end end  end 

the error due inside of loop never being reached, , therefore newdate , newph never defined inside of function. happening because aren't using i , j indices access single element of pressure_dbar , instead comparing entire array every time bound have some false values , if statement evaluate false.

really, should be

if (ge(pressure_dbar(i), minimum) && lt(pressure_dbar(i), maximum)) 

also, aren't storing results of internal loop array @ since overwrite values newph , newdate every time. second, you're better off using logical indexing generate newdate , newph

function [newdate, newph] = oceanphdepth(date, ph, pressure_dbar, minimum, maximum)     mask = pressure_dbar >= minimum & pressure_dbar < maximum;     newdate = date(mask);     newph = ph(mask); end