diff --git a/matlab/compute/compute_fluxtube_growth_rate.m b/matlab/compute/compute_fluxtube_growth_rate.m
deleted file mode 100644
index 2361236a30ceb6b907d15c155958e60887057b26..0000000000000000000000000000000000000000
--- a/matlab/compute/compute_fluxtube_growth_rate.m
+++ /dev/null
@@ -1,121 +0,0 @@
-function [ linear_gr ] = compute_fluxtube_growth_rate(DATA, OPTIONS)
-
-% Remove AA part
-if DATA.Nx > 1
- ikxnz = abs(DATA.PHI(1,:,1,1)) > 0;
-else
- ikxnz = abs(DATA.PHI(1,:,1,1)) > -1;
-end
-ikynz = (abs(DATA.PHI(:,1,1,1)) > 0);
-ikynz = logical(ikynz .* (DATA.ky > 0));
-phi = DATA.PHI(ikynz,ikxnz,:,:);
-t = DATA.Ts3D;
-
-[~,its] = min(abs(t-OPTIONS.TRANGE(1)));
-[~,ite] = min(abs(t-OPTIONS.TRANGE(end)));
-
-w_ky = zeros(sum(ikynz),ite-its);
-ce = zeros(sum(ikynz),ite-its);
-
-is = 1;
-% for it = its+1:ite
-% phi_n = phi(:,:,:,it);
-% phi_nm1 = phi(:,:,:,it-1);
-% dt = t(it)-t(it-1);
-% ZS = sum(sum(phi_nm1,2),3);
-%
-% wl = log(phi_n./phi_nm1)/dt;
-% w_ky(:,is) = squeeze(sum(sum(wl.*phi_nm1,2),3)./ZS);
-%
-% for iky = 1:numel(w_ky(:,is))
-% ce(iky,is) = abs(sum(sum(abs(w_ky(iky,is)-wl(iky,:,:)).^2.*phi_nm1(iky,:,:),2),3)./ZS(iky,:,:));
-% end
-% is = is + 1;
-% end
-%no sum over kx version
-ikx = 1;
-for it = its+1:ite
- phi_n = squeeze(phi(:,ikx,:,it));
- phi_nm1 = squeeze(phi(:,ikx,:,it-1));
- dt = t(it)-t(it-1);
- ZS = sum(phi_nm1,2); %sum over z
-
- wl = log(phi_n./phi_nm1)/dt;
- w_ky(:,is) = squeeze(sum(wl.*phi_nm1,2)./ZS);
-
- for iky = 1:numel(w_ky(:,is))
- ce(iky,is) = abs(sum(abs(w_ky(iky,is)-wl(iky,:)).^2.*phi_nm1(iky,:),2)./ZS(iky,:));
- end
- is = is + 1;
-end
-
-[kys, Is] = sort(DATA.ky(ikynz));
-
-linear_gr.OPTIONS.TRANGE = t(its:ite);
-linear_gr.g_ky = real(w_ky(Is,:));
-linear_gr.w_ky = imag(w_ky(Is,:));
-linear_gr.ce = abs(ce);
-linear_gr.ky = kys;
-linear_gr.std_g = std (real(w_ky(Is,:)),[],2);
-linear_gr.avg_g = mean(real(w_ky(Is,:)),2);
-linear_gr.std_w = std (imag(w_ky(Is,:)),[],2);
-linear_gr.avg_w = mean(imag(w_ky(Is,:)),2);
-
-if OPTIONS.NPLOTS >0
- figure
-if OPTIONS.NPLOTS > 1
- subplot(1,2,1)
-end
- x_ = linear_gr.ky;
- plt = @(x) x;
- OVERK = '';
- if OPTIONS.GOK == 1
- plt = @(x) x./x_;
- OVERK = '/$k_y$';
- elseif OPTIONS.GOK == 2
- plt = @(x) x.^2./x_.^3;
- OVERK = '/$k_y$';
- end
- plot(x_,plt(linear_gr.g_ky(:,end)),'-o','DisplayName',['$Re(\omega_{k_y})$',OVERK]); hold on;
- plot(x_,plt(linear_gr.w_ky(:,end)),'--*','DisplayName',['$Im(\omega_{k_y})$',OVERK]); hold on;
- plot(x_,plt(linear_gr.ce (:,end)),'x','DisplayName',['$\epsilon$',OVERK]); hold on;
-
- errorbar(linear_gr.ky,plt(linear_gr.avg_g),plt(linear_gr.std_g),...
- '-o','DisplayName','$Re(\omega_{k_y})$',...
- 'LineWidth',1.5); hold on;
- errorbar(linear_gr.ky,plt(linear_gr.avg_w),plt(linear_gr.std_w),...
- '--*','DisplayName','$Im(\omega_{k_y})$',...
- 'LineWidth',1.5); hold on;
-
-% xlim([min(linear_gr.ky) max(linear_gr.ky)]);
- xlabel('$k_y$');
- legend('show');
- title(DATA.param_title);
-
-if OPTIONS.NPLOTS > 1
- if OPTIONS.NPLOTS == 2
- subplot(1,2,2)
- elseif OPTIONS.NPLOTS == 3
- subplot(2,2,2)
- end
- plot(DATA.Ts3D(its+1:ite),linear_gr.g_ky(Is,:)); hold on;
- plot(DATA.Ts3D(its+1:ite),linear_gr.w_ky(Is,:));
- xlabel('t'); ylabel('$\gamma(t),\omega(t)$'); xlim([DATA.Ts3D(1) DATA.Ts3D(end)]);
-end
-
-if OPTIONS.NPLOTS > 2
- xlabel([]); xticks([]);
- subplot(2,2,4)
- [~,ikx0] = min(abs(DATA.kx));
- for i_ = 1:(DATA.Nkx+1)/2
- iky = 1 + (DATA.ky(1) == 0);
- ikx = ikx0 + (i_-1);
- semilogy(DATA.Ts3D,squeeze(abs(DATA.PHI(iky,ikx,DATA.Nz/2,:))),...
- 'DisplayName',['$k_x=',num2str(DATA.kx(ikx)),'$, $k_y=',num2str(DATA.ky(iky)),'$']);
- hold on;
- xlabel('t,'); ylabel('$|\phi_{ky}|(t)$')
- end
-legend('show')
-end
-
-end
\ No newline at end of file
diff --git a/matlab/compute/compute_growth_rates.m b/matlab/compute/compute_growth_rates.m
new file mode 100644
index 0000000000000000000000000000000000000000..a71f8f061557bce683e54bef6783cb20e90a3db7
--- /dev/null
+++ b/matlab/compute/compute_growth_rates.m
@@ -0,0 +1,36 @@
+function [w,e,t] = compute_growth_rates(field,time)
+% compute_growth_rates compute the linear growth rates using the amplitude
+% ratio method
+% see B.J. Frei et al. flux-tube paper
+% Input: (k1,k2,z,t) field
+% Output: w(k1,k2,t) the growth and frequencies w = gamma + i * omega
+% e(k1,k2) an error estimate of the convergence of w
+sz = size(field);
+N1 = sz(1); N2 = sz(2); Nz = sz(3); Nt = sz(4);
+
+
+w = zeros(N1,N2,Nt-1);
+e = zeros(N1,N2);
+for i1 = 1:N1
+ for i2 = 1:N2
+ to_measure = reshape(field(i1,i2,:,:),Nz,Nt);
+ % Amplitude ratio method for determining the growth rates and the
+ % frequencies
+ for it = 2:Nt
+ phi_n = to_measure(:,it);
+ phi_nm1 = to_measure(:,it-1);
+ dt = time(it)-time(it-1);
+ ZS = sum(phi_nm1,1); %sum over
+ wl = log(phi_n./phi_nm1)/dt;
+ w(i1,i2,it) = squeeze(sum(wl.*phi_nm1,1)./ZS);
+ end
+ % error estimation
+ wavg = mean(w(i1,i2,ceil(Nt/2):end));
+ wend = w(i1,i2,end);
+ e(i1,i2) = abs(wend-wavg)/abs(wavg);
+ end
+end
+
+t = time(2:Nt);
+
+end
\ No newline at end of file