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Mathematical modeling of procrastination was carried out on students in the Mathematics Department at Universitas Negeri Padang. Procrastination is the tendency to delay work and can be contagious among students. Mathematical modeling of procrastination aims to show the spread of procrastination among students. The SEIR compartment model was applied in this study. From a total of 1,154 population members, 93 samples were randomly selected and were given a questionnaire to estimate the parameter values in the model. A couple of steady states appear in the model. The free disease steady state has a biological meaning since all the variables are real, while the endemic steady state is surreal in biological terms. The number of its basic reproduction number, from which the parameter values are derived from the primary data, indicates stability analysis near the free disease steady states. The result shows that procrastination is spread among students in the population, with the number of Ro is 1,009.

Penelitian ini membahas tentang interaksi antara sel kanker dengan sel imun yang terdiri atas CTL dan sel T Helper, pada kasus kemoterapi. Model matematika dianalisis untuk memperoleh kestabilan lokal di sekitar titik ekuilibrium dengan menggunakan Matriks Jacobian. Analisis dilakukan pada kasus interaksi antara sel imun dan sel kanker dengan kemoterapi dan tanpa pemberian efek kemoterapi. Pada kasus tanpa kemoterapi diperoleh lima titik ekuilibrium yaitu tiga itik ekuilibrium bebas infeksi yang tidak stabil, satu titik ekuilibrium infeksi stabil dengan syarat tertentu, dan satu titik ekuilibrium infeksi yang stabil asimtotik. Sedangkan pada kasus kemoterapi diperoleh hasil yang lebih baik bagi penderita kanker yaitu terdapat enam titik ekuilibrium dimana dua titik ekulibrium bebas infeksi stabil asimtotik dengan syarat tertentu, satu titik ekulibirum bebas infeksi tidak stabil, dua titik ekulibrium infeksi stabil asimtotik dengan syarat tertentu dan satu titik ekulibrium infeksi stabil asimtotik.

The spread of tuberculosis can occur in two ways, namely exogenous and endogenous. The spread of tuberculosis exogenously or Exogenous Reinfection of tuberculosis can be observed using a mathematical model. Then an analysis of the mathematical model with a bifurcation approach was carried out. Based on the result, it was found that there was a change in stability properties and the type of equilibrium point in the distribution equation system of exogenous reinfection tuberculosis, where the parameter that occurred bifurcation was , with . When value of  is smaller than zero, the system of differential equations of exogenous reinfection tuberculosis shows an unstable with a saddle point type, when the value of     is equal to zero the system of differential equations cannot be determined its stability, and when  system of differential equations shows asymptotic stability, where there is a change in species. The points are nodes, star nodes, and spirals.

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