the mysterious for loop

okey, I am going to create a program that will find a specifit value in a graf

the distance:km i a 1:1000 vector. the y axis

spped_kmph is the same. the x axis

in this program i can put in a single value like 5 and i will find how fast the car was at that point

THE PROBLEM: i Want to put in a vector so i can find the speed at more than 1 point at the time but when i put in a vector i get the message ( Operands to the || and && operators must be convertible to logical scalar values. )

Can someone figure out the for loop i need to put in?

So if i put in a vecor x = [4:10] it will go throuh all those values one by one and in the end sopt out 6 values for ''v''

function v=velocity_(x, route)
load(route);
    index = findpos(distance_km', x);
%i need to put in a for loop here
    x1 = distance_km(index-1);
    x2 = distance_km(index);
    y1 = speed_kmph(index-1);
    y2 = speed_kmph(index);
v = y1 * (x-x2)./(x1-x2)+y2*(x-x1)./(x2-x1)
    end

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findpos is this function

------

function index = findpos(vector,val)
vMAX = length(vector);
x=1
if val < vector(1) || val > vector(vMAX)
    index = -1;
    
elseif val == vector(1)
    index = 2;
else
    while val > vector (x)
        x = x+1;
    end 
    index = x;
end 

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Star Strider]

The doubled logical operators are for scalar logical comparisons. Use single logical operators for vector comparisons. The any and all functions are also useful in this context.

[peter karlsson]

thanks! now there is just one problem left hehe

I need a for loop in the fist code...hmmmm

[Star Strider]

As always, my pleasure!

A for loop should be relatively straightforward to write to loop through the vector. You will need to index the variables that you want to return from the function, so for example:

for k = 1:numel(x)
    ... CODE ...
    v(k) = y1 * (x-x2)./(x1-x2)+y2*(x-x1)./(x2-x1)
end

[peter karlsson]

thanks again. I see now that it doesnt matther what i put in

If i write index = findpos(distance_km, 20:23) it will just take the first number (20) I guess that it is because i have index = x; in the bottum of the second code. Can i change that to something els so my index can be a vector?

[Star Strider]

As always, my pleasure.

I do not understand what you are doing.

I encourage you to experiment to see what works.

Answer 2

[Walter Roberson]

function index = findpos(vector, vals)
   index = interp1(vector, 1:length(vector), vals, 'previous');
   index(isnan(index)) = -1;
end