How do I loop through incrementally changing values

I have two given formulae,

a = 0.1+3*10^-3 * alpha^2

and

b= 0.2+0.1*alpha - (3*10^-3)(alpha^2)

I want to run through values of alpha that increase in small increments (0.5) from 1 to 20.

I need the results from those to then run through the formula c = tan^-1(a/b) which needs to be plotted for all the different inputs.

Answer 1

[Walter Roberson]

alphavals = 1:0.5:20;

for K = 1 : length(alphavals);
  alpha = alphavals(K);
  a = ...
  b = ...
  c(K) = atan2(b,a);
end

plot(alphavals, c);

Note that I adjusted to use the four-quadrant inverse tan; the formula as you wrote it would be only the two-quadrant inverse tan. You could create that if you really wanted:

c(K) = atan(a/b);

The code here shows what you asked, looping through changing the value of alpha. But it isn't nearly as efficient as it could be. Instead, you can use

alpha = 1:0.5:20;
temp = 3E-3 .* alpha.^2;    %notice the .^ instead of plain ^
a = 0.1 + temp;
b = 0.2 + 0.1 .* alpha - temp;
c = atan2(b, a);
plot(alpha, c);

Answer 2

[Nobel Mondal]

You could utilize the colon and element-wise operators, instead of looping.

For example:

alpha = 1:0.5:20;
a = 0.1 + 3* 10^-3 * alpha.^2

Answer 3

[David Sanchez]

alpha = 1:0.5:20;
a = 0.1+3*10^-3 * alpha.^2;
b = 0.2+0.1*alpha - (3*10^-3)*(alpha.^2);
c = 1./tan(-a./b); % I don't know what is your equation
plot3(a,b,c)