{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,21]],"date-time":"2026-01-21T14:24:41Z","timestamp":1769005481208,"version":"3.49.0"},"reference-count":27,"publisher":"World Scientific Pub Co Pte Ltd","issue":"06","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Int. J. Model. Simul. Sci. Comput."],"published-print":{"date-parts":[[2021,12]]},"abstract":"<jats:p> This work provides a new fuzzy variable fractional COVID-19 model and uses a variable fractional operator, namely, the fuzzy variable Atangana\u2013Baleanu fractional derivatives in the Caputo sense. Next, we explore the proposed fuzzy variable fractional COVID-19 model using the fixed point theory approach and determine the solution\u2019s existence and uniqueness conditions. We choose an appropriate mapping and with the help of the upper\/lower solutions method. We prove the existence of a positive solution for the proposed fuzzy variable fractional COVID-19 model and also obtain the result on the existence of a unique positive solution. Moreover, we discuss the generalized Hyers\u2013Ulam stability and generalized Hyers\u2013Ulam\u2013Rassias stability. Further, we investigate the results on maximum and minimum solutions for the fuzzy variable fractional COVID-19 model. <\/jats:p>","DOI":"10.1142\/s1793962321500598","type":"journal-article","created":{"date-parts":[[2021,8,26]],"date-time":"2021-08-26T15:37:21Z","timestamp":1629992241000},"page":"2150059","source":"Crossref","is-referenced-by-count":6,"title":["Positive solutions and stability of fuzzy Atangana\u2013Baleanu variable fractional differential equation model for a novel coronavirus (COVID-19)"],"prefix":"10.1142","volume":"12","author":[{"given":"Pratibha","family":"Verma","sequence":"first","affiliation":[{"name":"Department of Mathematics, Motilal Nehru National Institute of Technology Allahabad, Prayagraj 211004, Uttar Pradesh, India"}]},{"given":"Manoj","family":"Kumar","sequence":"additional","affiliation":[{"name":"Department of Mathematics, Motilal Nehru National Institute of Technology Allahabad, Prayagraj 211004, Uttar Pradesh, India"}]}],"member":"219","published-online":{"date-parts":[[2021,8,25]]},"reference":[{"issue":"2","key":"S1793962321500598BIB001","first-page":"157","volume":"7","author":"Yin X.","year":"2020","journal-title":"Int. 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