how i can select an indice in vector and matrix

Hello guys i have a problem to select an indice in matlab for ex: i have this programme:

T=[0 10 20 30 40 50]; % température en°C

phi=[0 20 40 60 80 100]; % Humidité relative en %

Cs =

    0.2685    0.3110    0.3501    0.3857    0.4192    0.4528
    0.2691    0.3079    0.3449    0.3785    0.4093    0.4368
    0.2690    0.3048    0.3394    0.3708    0.3991    0.4229
    0.2688    0.3025    0.3345    0.3635    0.3893    0.4107
    0.2692    0.3016    0.3313    0.3576    0.3806    0.3999
    0.2709    0.3031    0.3309    0.3538    0.3738    0.3900

we can imagine this like that

       0          10       20       30         40       50

 0    0.2685    0.3110    0.3501    0.3857    0.4192    0.4528
 20   0.2691    0.3079    0.3449    0.3785    0.4093    0.4368
 40   0.2690    0.3048    0.3394    0.3708    0.3991    0.4229
 60   0.2688    0.3025    0.3345    0.3635    0.3893    0.4107
 80   0.2692    0.3016    0.3313    0.3576    0.3806    0.3999
100   0.2709    0.3031    0.3309    0.3538    0.3738    0.3900

so i want to when i input temperature and humidity the programme select the Cs's value

for ex: if i do that

tx=input('chose your température plz')

phix=input('chose your humidity plz')

and i chose tx=10 & phix=20 the result will be

Csx=0.3079

i hope i explained my problem and i'm waiting your answers

[Cedric]

"Guys" actually ;-D

[ilyas ilyas]

i'm so sorry for my bed english lang

Answer 1

[Cedric]

If you are sure that phix and tx will be entered so they match exactly elements of T and phi, you can do the following:

 id_T   = find(T == tx) ;
 id_phi = find(phi == phix) ;

 Csx = Cs(id_phi, id_T) ;

If you aren't sure and you want to take the closest t and phi, you can do

 [~,id_T]   = min(abs(diff_T-tx)) ;
 [~,id_phi] = min(abs(phi-phix)) ;

 Csx = Cs(id_phi, id_T) ;

You could also interpolate, but that's another story.

[ilyas ilyas]

yah i wanna to interpolat and i have the eqt to calcul the Csx but i have a prob to select the indices if i have an value doesn't exict in vectors for ex: if i have tx= 22 & phix= 15 this values doesn't exict but i know by interpolation i use (1,3);(1,4);(2,3);(2,4) so how i can do that

[Cedric]

You can interpolate as follows

 [T_mesh, phi_mesh] = meshgrid(T, phi) ; 
 value = interp2(T_mesh, phi_mesh, Cs, tx, phix) ;

Answer 2

[ilyas ilyas]

yah i wanna to interpolat and i have the eqt to calcul the Csx but i have a prob to select the indices if i have an value doesn't exict in vectors for ex: if i have tx= 22 & phix= 15 this values doesn't exict but i know by interpolation i use (1,3);(1,4);(2,3);(2,4) so how i can do that

Answer 3

[ilyas ilyas]

for more explaine this pic will be do that

how i can select the indices plz

[Cedric]

This is essentially what INTERP2 does in my comment above, so there is little interest in re-implementing it by yourself (unless it is for a homework and you have to implement it by yourself).

So try using INTERP2; look up for examples in the official documentation and/or online if you need more than my example.

[ilyas ilyas]

hello it's not for a homework it's for my project:) i try to use the interp2 but the result is not the same

[Cedric]

At what point did you make the test and what/how did you compute.

The issue if you really want to implement your formula by hand is that you will have to manage quite a few special cases, which means that you will have to implement more code that just the formula that you have above.

Answer 4

[ilyas ilyas]

thank you Mr. Cedric the prob was finished

[Cedric]

Ok, great if you found a solution; bonne continuation !