Input value and compare to values in an array

clc, clear, clf

M1=input('What is the Mach number? ');

Mach=[1.050,1.1,1.2,1.3,1.4,1.6,1.8,2,2.5,3,4,5,6,7,8,10];

Maxd=[0.558,1.515,3.944,6.662,9.427,14.652,19.183,22.974,29.797,34.073,38.774,41.118,42,440,43.791,44.429];

So I have this as my code. What I want to do is take an input mach number, find the closest value in the Mach array (rounding down) and then use the corresponding index of the Maxd array for calculations. I'm sure this is simpler than I think it is but I would very much appreciate the help.

Answer 1

[Star Strider]

Using the interp1 (link) function:

M1=input('What is the Mach number? ');
Mach=[1.050,1.1,1.2,1.3,1.4,1.6,1.8,2,2.5,3,4,5,6,7,8,10];
Maxd=[0.558,1.515,3.944,6.662,9.427,14.652,19.183,22.974,29.797,34.073,38.774,41.118,42,440,43.791,44.429];
Result = interp1(Mach, Maxd, M1, 'previous')

M1 = 1.5
Result =
     9.427

You can easily change the interpolation method if you want a different result.

[Briana Staheli]

Thank you so much! this works like a charm!

[madhan ravi]

+1 cool method @star strider

[Star Strider]

As always, my pleasure!

Answer 2

[madhan ravi]

M1=input('What is the Mach number? ');

Mach=[1.050,1.1,1.2,1.3,1.4,1.6,1.8,2,2.5,3,4,5,6,7,8,10];

Maxd=[0.558,1.515,3.944,6.662,9.427,14.652,19.183,22.974,29.797,34.073,38.774,41.118,42,440,43.791,44.429];

[~,index]=min(abs(floor((Mach-(M1)))))  %floor rounds down towards negative infinity 

Maxd(index) %the value to be used in calculations

command window:

>> COMMUNITY
What is the Mach number? 3

index =

      10

ans =

     34.0730

[Stephan]

I think your code gives wrong result for input = 3

[madhan ravi]

check now @stephen

[Stephan]

Wrong result for 1.15 i think - OP want to rounding down

[Briana Staheli]

Thank you for the help!

Answer 3

[Stephan]

M1=input('What is the Mach number? ');
Mach=[1.050,1.1,1.2,1.3,1.4,1.6,1.8,2,2.5,3,4,5,6,7,8,10];
Maxd=[0.558,1.515,3.944,6.662,9.427,14.652,19.183,22.974,29.797,34.073,38.774,41.118,42,440,43.791,44.429];
Value = Maxd(find((sort([Mach, M1]))==M1,1,'last')-1)

[Briana Staheli]

Thank you this is great