use fzero to solve for a parameter

I wrote the following code to solve for a:

clear; clc;

EquivRatio = [0.64 0.74 0.84 0.94 1];

K = [0.371 0.447 0.456 0.383 0.302];

C_NO = [0.014 0.0179 0.0187 0.0139 0.0084];

R1 = [5.79*10^(-5) 0.00110 0.00877 0.0265 0.0235];

Tao_NO = C_NO./(4*R1);

t = 1;

fun = @(a)(1-K).*(log(1+a))-(1+K).*(log(1-a))-t./Tao_NO;

alpha = fzero(fun,0.008229);

But it always give the following error:

Operands to the and && operators must be convertible to logical scalar values.

Error in fzero (line 322) elseif ~isfinite(fx) ~isreal(fx)

What's wrong with my code?

[Diego Leal]

I seems that you are trying to find the zeros from a function that goes from scalar to vector. Is that what you want to do?

[Ivy Shen]

Hi,I want to solve for a.

[Kevin Chng]

Hi Ivy Shen,

As I see your code, there are 5 equations to solve a. Therefore, we should load a for loop to solve them one by one

clear; clc;

EquivRatio = [0.64 0.74 0.84 0.94 1];

K = [0.371 0.447 0.456 0.383 0.302];

C_NO = [0.014 0.0179 0.0187 0.0139 0.0084];

R1 = [5.79*10^(-5) 0.00110 0.00877 0.0265 0.0235];

Tao_NO = C_NO./(4*R1);

t = 1;

for i=1:1:length(K)
fun = @(a)(1-K(i)).*(log(1+a))-(1+K(i)).*(log(1-a))-t./Tao_NO(i);
alpha(i) = fzero(fun,0.008229);
end

I'm not sure whether i interpret your question correctly, let us know, if my recommendation is workout for you.

[Ivy Shen]

Thank you! But it gives two NaN values as shown below. Do you know what's wrong with it?

[Kevin Chng]

You have to change 0.008229 value.

[Kevin Chng]

for i=1:1:length(K)
fun = @(a)(1-K(i)).*(log(1+a))-(1+K(i)).*(log(1-a))-t./Tao_NO(i);
figure
fplot(fun,[-2 2])
alpha(i) = fzero(fun,0.999);
end

Hi, you may use fplot to view how is your graph's pattern. From the graph, you may see the value is leading to 1 when approaching zero for 4 & 5.

When i change the initial value to 0.999, i find the root for 4.

[Ivy Shen]

Thank you very much!

Answer 1

[Kevin Chng]

Hi Ivy Shen,

As I see your code, there are 5 equations to solve a. Therefore, we should load a for loop to solve them one by one

clear; clc;
EquivRatio = [0.64 0.74 0.84 0.94 1];
K = [0.371 0.447 0.456 0.383 0.302];
C_NO = [0.014 0.0179 0.0187 0.0139 0.0084];
R1 = [5.79*10^(-5) 0.00110 0.00877 0.0265 0.0235];
Tao_NO = C_NO./(4*R1);
t = 1;
for i=1:1:length(K)
fun = @(a)(1-K(i)).*(log(1+a))-(1+K(i)).*(log(1-a))-t./Tao_NO(i);
alpha(i) = fzero(fun,0.008229);
end

you may use fplot to view how is your graph's pattern. From the graph, you may see the value is leading to 1 when approaching zero for 4 & 5.

for i=1:1:length(K)
fun = @(a)(1-K(i)).*(log(1+a))-(1+K(i)).*(log(1-a))-t./Tao_NO(i);
figure
fplot(fun,[-2 2])
alpha(i) = fzero(fun,0.999);
end