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Desimal: Jurnal Matematika
Published by Universitas Islam Negeri Raden Intan Lampung
ISSN : 26139073     EISSN : 26139081     DOI : -
Core Subject : Education, Social,
Education Mathematics Social Sciences
Desimal: Jurnal Matematika, particularly focuses on the main issues in the development of the sciences of mathematics education, mathematics education, and applied mathematics. Desimal: Jurnal Matematika published three times a year, the period from January to April, May to Augustus, and September to December. This publication is available online via open access.
Arjuna Subject : -
Articles 337 Documents
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Forecasting Oil Palm Production Using ARIMA Time Series Model with Rainfall Indicators in Mesuji Regency
Desimal: Jurnal Matematika Vol. 9 No. 1 (2026): Desimal: Jurnal Matematika
Publisher : Universitas Islam Negeri Raden Intan Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24042/djm.v9i1.30063

Abstract

Oil palm production is a key driver of regional economic resilience in Indonesia, yet its predictability remains highly uncertain due to climate variability, particularly rainfall fluctuations. Although time series forecasting models such as ARIMA are widely applied, prior studies largely treatenvironmental variables as external factors rather than integrating them into a structured analytical interpretation. This study addresses this limitation by developing an environmentally-informed forecasting framework that explicitly links rainfall dynamics with oil palm production patterns using the Autoregressive Integrated Moving Average (ARIMA) approach. Secondary data from 2005 to 2024 were analyzed through a rigorous Box–Jenkins procedure, including stationarity testing, model identification, parameter estimation, and diagnostic validation. The results demonstrate that ARIMA (1,2,1) provides the most consistent representation of production dynamics, while ARIMA (0,2,2) captures rainfall variability. Forecasting results reveal a stable production trajectory over the next five years despite declining rainfall trends, indicating a decoupling pattern between environmental variability and production output. Furthermore, correlation analysis confirms a weak negative relationship, suggesting that excessive rainfall may disrupt production efficiency rather than enhance it. This study advances the existing literature by reframing time series forecasting as an integrated environmental–production system rather than a purely statistical exercise. The findings offer both methodological insight and practical relevance for improving adaptive decision-making in climate-sensitive agricultural systems
Evaluation of Lock Cover and STEM Dimensional Variations on Separation Force Using Multiple Regression and Statistical Process Control
Desimal: Jurnal Matematika Vol. 9 No. 1 (2026): Desimal: Jurnal Matematika
Publisher : Universitas Islam Negeri Raden Intan Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24042/djm.v9i1.30842

Abstract

This study addresses a critical limitation in conventional manufacturing analysis by demonstrating that dimensional variation in injection-molded press-fit systems should be interpreted as an interaction-driven phenomenon rather than independent geometric effects. The research focuses on lock stem and cover dimensions produced in a multi-cavity injection molding system, where geometric dependency leads to strong multicollinearity among variables. A quantitative approach was applied using actual production data, including dimensional measurements and separation force testing. Multiple linear regression was employed to model the relationship between geometric parameters and mechanical performance, supported by classical assumption testing and multicollinearity diagnostics. The results indicate a very high coefficient of determination, showing that dimensional variation collectively explains most of the separation force variability. However, severe multicollinearity limits the reliability of individual parameter interpretation and highlights the need for system-level analysis. Statistical Process Control confirms that the process operates within stable limits, while process capability analysis shows compliance with specification requirements. Despite this, variation in separation force persists, indicating high sensitivity to small geometric deviations. These findings emphasize that process stability alone is insufficient to ensure consistent performance. This study introduces an integrated framework combining regression, SPC, and capability analysis, providing both theoretical insight and practical guidance for improving dimensional control in precision manufacturing.
Analysis of the Impact of Changes in the Indonesian Mortality Table III to IV on Life Insurance Premiums Using the Gompertz–Makeham Model Approach
Desimal: Jurnal Matematika Vol. 9 No. 1 (2026): Desimal: Jurnal Matematika
Publisher : Universitas Islam Negeri Raden Intan Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24042/djm.v9i1.30906

Abstract

Life insurance premium determination is highly sensitive to mortality assumptions, which are typically represented through actuarial mortality tables. The transition from the Indonesian Mortality Table III (2011) to Table IV (2019) reflects structural shifts in population mortality that may alter both actuarial valuation and model behavior. Despite its importance, limited research has examined how such changes influence premium outcomes within a continuous mortality modeling framework. This study aims to investigate the impact of mortality table transitions on life insurance premiums using the Gompertz–Makeham model, with particular emphasis on parameter sensitivity and model consistency. Secondary data of age-specific mortality probabilities for individuals aged 20–60 years, classified by gender, were transformed into continuous mortality rates and estimated using numerical optimization techniques. Model performance was assessed through the alignment between observed and fitted mortality patterns, as well as the exponential growth structure implied by the model. Premium calculations were conducted using the net single premium approach under a constant interest rate assumption. The results show that the updated mortality table systematically reduces premium values by a measurable margin, with stronger effects observed at older ages. Furthermore, the findings reveal that parameter changes significantly influence the stability and responsiveness of the mortality model. This study contributes by offering a quantitative sensitivity-based framework that integrates mortality table transitions into continuous actuarial modeling, thereby enhancing the accuracy and reliability of premium estimation.
Comparison of Whole Life Insurance Premiums Based on the De Moivre Mortality Model and the Indonesian Mortality Table 2019
Desimal: Jurnal Matematika Vol. 9 No. 1 (2026): Desimal: Jurnal Matematika
Publisher : Universitas Islam Negeri Raden Intan Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24042/djm.v9i1.30928

Abstract

This study examines the mathematical structure and sensitivity of whole life insurance premium calculations under two distinct mortality assumptions, namely the De Moivre mortality model and the Indonesian Mortality Table 2019 (TMI 2019). Moving beyond conventional numerical comparisons, this research focuses on identifying structural bias and model-driven deviations in actuarial valuation. A quantitative analytical approach is employed by computing the Net Single Premium (NSP) for entry ages of 25, 30, and 40 years, incorporating variations in the limiting age parameter to evaluate the responsiveness of the De Moivre model. The results demonstrate that the De Moivre model consistently produces higher premiums due to its uniform mortality assumption, which systematically overestimates early-age death probabilities relative to empirical data. Furthermore, the deviation pattern is shown to be non-linear and convergent, where the magnitude of difference decreases with increasing age and limiting age, indicating asymptotic alignment between theoretical and empirical mortality structures. This finding reveals the presence of inherent bias in simplified mortality laws and highlights their limitations in accurately representing real population dynamics. From a mathematical perspective, this study provides a sensitivity-based interpretation of mortality assumptions and establishes a consistent relationship between model structure and premium distortion. Therefore, the results contribute both theoretically, by clarifying the behavior of mortality-based actuarial models, and practically, by informing more reliable model selection in insurance premium estimation.
K-Nearest Neighbor-Based Forecasting of Human Ascariasis Using Profile-Driven Risk Indicators
Desimal: Jurnal Matematika Vol. 9 No. 1 (2026): Desimal: Jurnal Matematika
Publisher : Universitas Islam Negeri Raden Intan Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24042/djm.v9i1.30642

Abstract

This study addresses a critical limitation in ascariasis surveillance by introducing a mathematical modeling framework based on non-laboratory diagnostic indicators for early risk prediction in resource-constrained settings. Conventional detection methods rely heavily on laboratory diagnostics, which are often inaccessible in rural healthcare systems, leading to delayed intervention and persistent transmission. To overcome this challenge, the study develops a K-nearest neighbors (KNN) model interpreted as a distance-based classification approach within an epidemiological risk space, where similarity reflects shared exposure patterns among individuals. The model utilizes secondary data from 315 cases with laboratory-confirmed outcomes and incorporates key variables including sex, body mass index, livestock exposure, waste disposal practices, and environmental risk factors. Model performance was evaluated using 10-fold cross-validation across multiple configurations (k = 1, 3, 5, 7, 9) and assessed through AUC, accuracy, precision, recall, F1-score, and Matthews correlation coefficient. The results demonstrate that the k = 9 configuration achieves the most balanced performance, with an AUC of 0.924 and F1-score of 0.852, indicating strong discriminative capability and classification stability. The study contributes to epidemiological risk modeling by formalizing KNN within a structured risk-space interpretation and demonstrates that non-laboratory indicators can support reliable prediction. This approach offers a computationally efficient and interpretable tool for rural health surveillance and data-driven decision-making.
Digital Literacy Skills: A Sine Qua Non for Effective Teaching Practice Supervision of Mathematics Education Pre-service Teachers in an Open Distance and e-Learning Environment
Desimal: Jurnal Matematika Vol. 9 No. 1 (2026): Desimal: Jurnal Matematika
Publisher : Universitas Islam Negeri Raden Intan Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24042/djm.v9i1.30839

Abstract

The rapid expansion of digital learning environments in mathematics education has revealed fundamental limitations in how teaching practice supervision is conceptualized and implemented, particularly within Open Distance and e-Learning (ODeL) contexts where conventional supervisory models are increasingly inadequate. This study critically examines the role of digital literacy in shaping supervision practices and advances an integrated conceptual framework that links digital competencies with supervisory processes. A systematic literature review was conducted through a structured selection of ten studies, enabling a rigorous thematic synthesis of recurring patterns and relationships. The findings demonstrate that digital literacy operates as a multidimensional construct encompassing technical, pedagogical, communicative, and assessment-related competencies that collectively redefine how supervision is enacted in digitally mediated learning environments. The analysis further reveals that the effectiveness of digital literacy is inherently conditional, shaped by the interplay of infrastructure, institutional support, and professional training, thereby challenging assumptions that technological adoption alone enhances supervision quality. In addition, the study exposes a persistent fragmentation in the literature, where digital literacy and supervision are often treated as disconnected domains. Addressing this gap, this study advances a systemic and interactional framework that captures the dynamic relationships between digital literacy, supervision practices, and contextual conditions. This framework not only contributes to theoretical refinement but also provides a robust foundation for rethinking supervision in mathematics education within increasingly digitalized learning systems.
The Effectiveness of Ethnomathematics-Based Problem Based Learning (PBL) Model on Junior High School Students' Mathematical Problem-Solving Ability
Desimal: Jurnal Matematika Vol. 9 No. 1 (2026): Desimal: Jurnal Matematika
Publisher : Universitas Islam Negeri Raden Intan Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24042/djm.v9i1.30940

Abstract

The persistent challenge of developing students’ mathematical problem-solving ability highlights the need for instructional approaches that move beyond procedural learning toward meaningful and contextually grounded understanding. This study investigates the effectiveness of integrating ethnomathematics within a Problem-Based Learning (PBL) framework to enhance students’ mathematical problem-solving ability. A quasi-experimental design with a nonequivalent control group was employed involving 64 ninth-grade students at SMP Negeri 1 Bajawa, Indonesia. The experimental group was taught using ethnomathematics-based PBL, while the control group received conventional instruction. Data were collected through validated essay-based tests and analyzed using descriptive statistics and an independent samples t-test. The findings reveal that the experimental group achieved a substantially higher mean posttest score (84.06) compared to the control group (72.44), with the difference proven to be statistically significant (p < 0.05). Furthermore, the large effect size indicates that the intervention produced not only statistical significance but also meaningful educational impact. These results suggest that the integration of cultural context within a structured problem-based learning environment facilitates deeper cognitive engagement, enabling students to interpret, represent, and solve mathematical problems more effectively. The study advances existing literature by demonstrating that ethnomathematics functions as a cognitive catalyst when embedded within inquiry-driven pedagogy, rather than as a supplementary contextual element. In conclusion, ethnomathematics-based PBL offers a robust and contextually responsive instructional model that supports the development of higher-order thinking skills and provides a viable pathway for improving the quality of mathematics education.

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