Density-Temperature diagram

I have this semilog diagram with temperature (y axis) and viscosity(x axis). The diagram is linear. Chosen one type of oil, I need an equation that returns viscosity's values entering a particular value of temperature. How can i do? I've tried something like this, but it's totally wrong:

x =[10,50];

y =[50,0];

C = polyfit(log10(x),y,1);

m = C(1);

k = C(2);

T = 100;

vi = polyval(C,log10(x))

[Rafael Hernandez-Walls]

x =[10,50];
y =[50,0];
C = polyfit(log10(x),y,1);
m = C(1);
k = C(2);
T = 100;
vi = polyval(C,log10(x))

Answer 1

[Alan Stevens]

Perhaps you should have T instead of x in the last line (and have you got the two parameters the wrong way round? You want to get viscosity (x) from temperature (y)).. Also look up interp1.

x =[10,50];
y =[50,0];
C = polyfit(y,log10(x),1);
m = C(1);
k = C(2);
T = 100;
vi = polyval(C,T);
vi = 10^vi;